U.S. patent number 5,130,242 [Application Number 07/580,778] was granted by the patent office on 1992-07-14 for process for the heterotrophic production of microbial products with high concentrations of omega-3 highly unsaturated fatty acids.
This patent grant is currently assigned to Phycotech, Inc.. Invention is credited to William R. Barclay.
United States Patent |
5,130,242 |
Barclay |
July 14, 1992 |
**Please see images for:
( Certificate of Correction ) ** |
Process for the heterotrophic production of microbial products with
high concentrations of omega-3 highly unsaturated fatty acids
Abstract
A process for the heterotrophic or predominantly heterotrophic
production of whole-celled or extracted microbial products with a
high concentration of omega-3 highly unsaturated fatty acids,
producible in an aerobic culture under controlled conditions using
biologically pure cultures of heterotrophic single-celled fungi
microorganisms of the order Thraustochytriales. The harvested
whole-cell microbial product can be added to processed foods as a
nutritional supplement, or to fish and animal feeds to enhance the
omega-3 highly unsaturated fatty acid content of products produced
from these animals. The lipids containing these fatty acids can
also be extracted and used in nutritional, pharmaceutical and
industrial applications.
Inventors: |
Barclay; William R. (Boulder,
CO) |
Assignee: |
Phycotech, Inc. (Boulder,
CO)
|
Family
ID: |
27031913 |
Appl.
No.: |
07/580,778 |
Filed: |
September 11, 1990 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
439093 |
Nov 17, 1989 |
|
|
|
|
241410 |
Sep 7, 1988 |
|
|
|
|
Current U.S.
Class: |
435/134; 426/49;
426/601; 426/53; 435/243; 435/946 |
Current CPC
Class: |
A61K
31/20 (20130101); C11B 1/10 (20130101); C12N
1/14 (20130101); C12P 7/6427 (20130101); C12P
7/6445 (20130101); C12P 7/6472 (20130101); A23K
10/16 (20160501); A23K 20/158 (20160501); A23K
50/00 (20160501); A23K 50/10 (20160501); A23K
50/75 (20160501); A23K 50/80 (20160501); A23L
29/065 (20160801); A23L 11/07 (20160801); A23L
19/09 (20160801); A23L 33/12 (20160801); A23L
13/00 (20160801); A23L 13/43 (20160801); A23L
13/50 (20160801); A23L 15/20 (20160801); A23L
17/00 (20160801); A23L 17/40 (20160801); A23L
25/30 (20160801); A61K 31/202 (20130101); Y02A
40/818 (20180101); Y10S 435/946 (20130101) |
Current International
Class: |
A23L
1/20 (20060101); A23L 1/30 (20060101); A23L
1/325 (20060101); A23K 1/00 (20060101); A23K
1/16 (20060101); A23L 1/03 (20060101); A23K
1/18 (20060101); A23L 1/315 (20060101); A23L
1/212 (20060101); A23L 1/36 (20060101); A23L
1/31 (20060101); A23L 1/32 (20060101); A23L
1/33 (20060101); A23L 1/314 (20060101); A61K
31/20 (20060101); A61K 31/185 (20060101); A61K
31/202 (20060101); C11B 1/10 (20060101); C11B
1/00 (20060101); C12N 1/14 (20060101); C12P
7/64 (20060101); C12P 007/64 (); C12N 001/00 ();
A23B 007/10 (); A23D 009/00 () |
Field of
Search: |
;435/134,243,946
;426/49,53,601 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Tornabene et al., Sterols, Aliphatic Hydrocarbons, and Fatty Acids
of a Nonphotosynthetic Diatom, Nitzchia alba, Lipids,
9/4:279(1974). .
Harrington and Holz, The Monoenoic and Docosahexaenoic Fatty Acids
of a Heterotrophic Dinoflagellate, Biochim. Biophys. Acta,
164:137(1968). .
Haskins et al., Steroids and the Stimulation of Sexual Reproduction
of a Species of Pythium, Canadian J. Microbiology, 10:187(1964).
.
Orcutt and Patterson, Sterol, Fatty Acid and Elemental Composition
of Diatoms Grown in Chemically Defined Media, Comp. Biochem.
Physiol., 50B:579(1975). .
Emerson, R. (1950) Ann. Rev. Micro. 4;169-200. .
Erwin, J. (1973) In Lipids and Biomembranes of Eukaryotic
Microorganisms, J. Erwin (ed.), Academic Press, New York, pp.
41-143. .
Findlay, R. H. et al. (1986) in the Biology of Marine Fungi, S. T.
Moss (ed)., Cambridge University Press, London, pp. 91-103. .
Fuller, M. S. et al. (1964) Mycologia 56:745-756. .
Goldstein, S. (1963) Am. J. Bot. 50:271-279. .
Pohl, P. and Zurheide, F. (1979) In Marine Algae in Pharmaceutical
Science, H. Hoppe et al., (eds.), W. de Gruyter, Berlin, pp.
473-524. .
Ryther, J. H. (1983) In Solar Energy Research Inst. Aquatic Species
Program Rev. Proc. Mar. 1983 Principal Investigators Meeting,
SERI/CP-231-1946, pp. 79-88. .
Schneider, J. (1976) In Marine Ecology, vol. 3, Part 1,
Cultivation, O. Kinne (ed), Wiley Interscience, London, pp.
339-345. .
Sparrow, F. K. (1960) Aquatic Phycomycetes, University of Michigan
Press, Ann Arbor, pp. 37-38. .
Weete, J. D. (1980) In Lipid Biochemistry of Fungi and Other
Organisms, Chapter 3, Plenum Press, New York. .
Wassef, M. (1977) Adv. Lipid Res. 15:159-232. .
Yamada, H. et al. (1987) J. Am. Oil Chemists Soc. 64:1254. .
Miller, C. E. (1967) Mycologiz 59:524-527. .
Ellenbogen et al., Comp. Biochem. Physiol., vol. 29, pp. 805-811,
1969. .
Kyle, JAOCS, vol. 64, No. 9, p. 1251, 1987..
|
Primary Examiner: Robinson; Douglas W.
Assistant Examiner: Ware; Deborah K.
Attorney, Agent or Firm: Sheridan, Ross & McIntosh
Parent Case Text
Cross-Reference to Related Applications
This application is a continuation-in-part of copending and
commonly assigned U.S. patent application Ser. No. 07/439,093,
filed Nov. 17, 1989, and entitled "Process for Heterotrophic
Production of Microbial Products with High Concentrations of
Omega-3 Highly Unsaturated Fatty Acids" now abandoned which is
incorporated herein in its entirety by reference and is a
continuation-in-part of U.S. patent application Ser. No.
07/241,410, filed Sept. 7, 1988, and entitled "Process for
Heterotrophic Production of Microbial Products with High
Concentrations of Omega-3 Highly Unsaturated Fatty Acids" which was
previously expressly abandoned.
Claims
What is claimed is:
1. A food product, comprising:
a) microorganisms selected from the group consisting of
microorganisms of the genus Thraustochytrium, microorganisms of the
genus Schizochytrium and mixtures thereof, wherein said
microorganisms are capable of effectively producing omega-3 highly
unsaturated fatty acid under conditions comprising:
i) salinity levels less than salinity levels found in seawater;
and
ii) a temperature of at least about 15.degree. C.; and
b) food material.
2. A food product, as claimed in claim 1, wherein said food
material is animal food.
3. A food product, as claimed in claim 1, wherein said food
material is human food.
4. A food product, as claimed in claim 1, further comprising an
antioxidant added to a fermentation medium prior to harvesting of
said microorganisms or added to said food product during
post-harvest processing of said microorganisms.
5. A food product, as claimed in claim 1, wherein said food product
is packaged under non-oxidizing conditions.
6. A food product, as claimed in claim 1, wherein said food product
is extruded to manipulate by degree of cell rupture the
bioavailability of omega-3 highly unsaturated fatty acids contained
in said microorganisms.
7. A food product, as claimed in claim 1, wherein said food product
is extruded to reduce the amount of oxygen that reaches the omega-3
highly unsaturated fatty acid as compared to the amount of oxygen
that would reach the omega-3 highly unsaturated fatty acid in an
analogous food product which has not been extruded.
8. A food product, as claimed in claim 1, wherein said
microorganisms have been cultured in a medium comprising a sodium
concentration less than about 6.58 g/l.
9. A food product, as claimed in claim 1, wherein said
microorganisms have been cultured in a medium comprising a sodium
concentration less than about 4.61 g/l.
10. A food product, as claimed in claim 1, wherein said
microorganisms are selected from the group consisting of:
(i) Schizochytrium having the identifying characteristics of ATCC
Accession No. 20888 and mutant strains derived therefrom, wherein,
said mutant strains derived therefrom are capable of producing
omega-3 highly unsaturated fatty acid;
(ii) Schizochytrium having the identifying characteristics of ATCC
Accession No. 20889 and mutant strains derived therefrom, wherein,
said mutant strains derived therefrom are capable of producing
omega-3 highly unsaturated fatty acid;
(iii) Thraustochytrium having the identifying characteristics of
ATCC Accession No. 20890 and mutant strains derived therefrom,
wherein, said mutant strains derived therefrom are capable or
producing omega-3 highly unsaturated fatty acid;
(iv) Thraustochytrium having the identifying characteristics of
ATCC Accession No. 20891 and mutant strains derived therefrom,
wherein, said mutant strains derived therefrom are capable of
producing omega-3 highly unsaturated fatty acid; and
(v) Thraustochytrium having the identifying characteristics of ATCC
Accession No. 20892 and mutant strains derived therefrom, wherein,
said mutant strains derived therefrom are capable of producing
omega-3 highly unsaturated fatty acid.
Description
FIELD OF THE INVENTION
The field of this invention relates to heterotrophic organisms and
a process for culturing them for the production of lipids with high
concentrations of omega-3 highly unsaturated fatty acids (HUFA)
suitable for human and animal consumption as food additives or for
use in pharmaceutical and industrial products.
BACKGROUND OF THE INVENTION
Omega-3 highly unsaturated fatty acids are of significant
commercial interest in that they have been recently recognized as
important dietary compounds for preventing arteriosclerosis and
coronary heart disease, for alleviating inflammatory conditions and
for retarding the growth of tumor cells. These beneficial effects
are a result both of omega-3 highly unsaturated fatty acids causing
competitive inhibition of compounds produced from omega-6 fatty
acids, and from beneficial compounds produced directly from the
omega-3 highly unsaturated fatty acids themselves (Simopoulos et
al., 1986). Omega-6 fatty acids are the predominant highly
unsaturated fatty acids found in plants and animals. Currently the
only commercially available dietary source of omega-3 highly
unsaturated fatty acids is from certain fish oils which can contain
up to 20-30% of these fatty acids. The beneficial effects of these
fatty acids can be obtained by eating fish several times a week or
by daily intake of concentrated fish oil. Consequently large
quantities of fish oil are processed and encapsulated each year for
sale as a dietary supplement.
However, there are several significant problems with these fish oil
supplements. First, they can contain high levels of fat-soluble
vitamins that are found naturally in fish oils. When ingested,
these vitamins are stored and metabolized in fat in the human body
rather than excreted in urine. High doses of these vitamins can be
unsafe, leading to kidney problems or blindness and several U.S.
medical associations have cautioned against using capsule
supplements rather than real fish. Secondly, fish oils contain up
to 80% of saturated and omega-6 fatty acids, both of which can have
deleterious health effects. Additionally, fish oils have a strong
fishy taste and odor, and as such cannot be added to processed
foods as a food additive, without negatively affecting the taste of
the food product. Moreover, the isolation of pure omega-3 highly
unsaturated fatty acids from this mixture is an involved and
expensive process resulting in very high prices ($200-$1000/ g) for
pure forms of these fatty acids (Sigma Chemical Co., 1988;
CalBiochem Co., 1987).
The natural source of omega-3 highly unsaturated fatty acids in
fish oil is algae. These highly unsaturated fatty acids are
important components of photosynthetic membranes. Omega-3 highly
unsaturated fatty acids accumulate in the food chain and are
eventually incorporated in fish oils. Bacteria and yeast are not
able to synthesize omega-3 highly unsaturated fatty acids and only
a few fungi are known which can produce minor and trace amounts of
omega-3 highly unsaturated fatty acids (Weete, 1980; Wassef, 1977;
Erwin, 1973).
Algae have been grown in outdoor cultivation ponds for the
photoautotrophic production of a wide variety of products including
omega-3 highly unsaturated fatty acid containing biomass. For
example, U.S. Pat. No. 4,341,038 describes a method for the
photosynthetic production of oils from algae, and U.S. Pat. No.
4,615,839 describes a process for concentrating eicosapentaenoic
acid (EPA) (one of the omega-3 highly unsaturated fatty acids)
produced photosynthetically by strains of the green algal
Chlorella. Photoautotrophy is the process whereby cells utilize the
process of photosynthesis to construct organic compounds from
CO.sub.2 and water, while using light as an energy source. Since
sunlight is the driving force for this type of production system,
algal cultivation ponds require large amounts of surface area
(land) to be economically viable. Due to their large size, these
systems cannot be economically covered, because of high costs and
technical problems, and because even transparent covers tend to
block a significant amount of the sunlight. Therefore, these
production systems are not axenic, and are difficult to maintain as
monocultures. This is especially critical if the cultures need to
be manipulated or stressed (e.g. nitrogen limited) to induce
production of the desired product. Typically, it is during these
periods of stress, when the cells are only producing product and
are not multiplying, that contaminants can readily invade the
cultures. Thus, in most cases, the biomass produced is not
desirable as a food additive for human consumption without
employing expensive extraction procedures to recover the lipids.
Additionally, photosynthetic production of algae in outdoor systems
is very costly, since cultures must be maintained at low densities
(1-2 g/l) to prevent light limitation of the culture. Consequently,
large volumes of water must be processed to recover small
quantities of algae, and since the algal cells are very tiny,
expensive harvesting processes must also be employed.
Mixotrophy is an alternative mode of production whereby certain
strains of algae carry on photosynthesis with light as a necessary
energy source but additionally use organic compounds supplied in
the medium. Higher densities can be achieved by mixotrophic
production and the cultures can be maintained in closed reactors
for axenic production. U.S. Pat. Nos. 3,444,647 and 3,316,674
describe processes for the mixotrophic production of algae.
However, because of the need to supply light to the culture,
production reactors of this type are very expensive to build and
operate, and culture densities are still very limited.
An additional problem with the cultivation of algae for omega-3
highly unsaturated fatty acid production, is that even though
omega-3 highly unsaturated fatty acids comprise 20-40% of some
strains, total fatty acids, the total fatty acid content of these
algae is generally very low, ranging from 5-10% of ash-free dry
weight. In order to increase the fatty acid content of the cells,
they must undergo a period of nitrogen limitation which stimulates
the production of lipids. However, of all the strains noted to date
in the literature, and over 60 strains evaluated by the inventor,
all exhibit a marked decrease in omega-3 highly unsaturated fatty
acids as a percentage of total fatty acids, when undergoing
nitrogen limitation (Erwin, 1973; Pohl & Zurheide, 1979).
With respect to economics and to utilizing omega-3 highly
unsaturated fatty acids as a food additive, it would be desirable
to produce these fatty acids in a heterotrophic culture.
Heterotrophy is the capacity for sustained and continuous growth
and cell division in the dark in which both energy and cell carbon
are obtained solely from the metabolism of an organic substrate(s).
Since light does not need to be supplied to a heterotrophic
culture, the cultures can be grown at very high densities in closed
reactors. Heterotrophic organisms are those which obtain energy and
cell carbon from organic substrates, and are able to grow in the
dark. Heterotrophic conditions are those conditions that permit the
growth of heterotrophic organisms, whether light is present or not.
However, the vast majority of algae are predominantly
photoautotrophic, and only a few types of heterotrophic algae are
known. U.S. Pat. Nos. 3,142,135 and 3,882,635 describe processes
for the heterotrophic production of protein and pigments from algae
such as Chlorella, Spongiocuccum, and Prototheca. However these
genera and others that have been documented to grow very well
heterotrophically (e.g. Scenedesmus), do not produce omega-3 highly
unsaturated fatty acids (Erwin, 1973). The very few heterotrophic
algae known to produce any omega-3 highly unsaturated fatty acids
(e.g., apochlorotic diatoms or apochlorotic dinoflagellates)
generally grown slowly and produce low amounts of omega-3 highly
unsaturated fatty acids as a percentage of ash-free dry weight
(Harrington and Holtz, 1968; Tornabene et al., 1974).
A few higher fungi are known to produce omega-3 highly unsaturated
fatty acids, but they comprise only a very small fraction of the
total fatty acids in the cells (Erwin, 1973; Wassef, 1977; Weete,
1980). As such, they would not be good candidates for commercial
production of omega-3 highly unsaturated fatty acids. For example,
Yamada et al. (1987) recently reported on the cultivation of
several species of the fungus, Mortierella, (isolated from soils)
for the production of the omega-6 fatty acid, arachidonic acid.
These fungi also produce small amounts of omega-3 eicosapentaenoic
acid along with the arachidonic acid when grown at low temperatures
(5.degree.-24.degree. C.). However, the resulting eicosapentaenoic
acid content was only 2.6% of the dry weight of the cells, and the
low temperatures necessary to stimulate production of this fatty
acid in these species would result in greatly decreased
productivities (and economic potential) of the cultivation system.
Some single-celled members of the order Thraustochytriales are also
known to produce omega-3 highly unsaturated fatty acids
(Ellenbogen, 1969, Wassef, 1977; Weete, 1980; Findlay et al.. 1986)
but they are known to be difficult to culture. Sparrow (1960) noted
that the minuteness and simple nature of the thalli of the family
Thraustochytriaceae (order Thraustochytriales) make them
exceedingly difficult to propagate. Additional reasons for this
difficulty have been outlined by Emerson (1950) and summarized by
Schneider (1976): "1) these fungi consist of very small thalli of
only one or a few cells, which generally grow very slowly in
culture, and are very sensitive to environmental perturbation; 2)
they are generally saprophytes, or parasites with very specialized
nutritional and environmental demands; and 3) in pure culture they
generally exhibit restricted growth, with vegetative growth
terminating after a few generations." (Although some prior art
classifies the thraustochytrids as fungi, the most recent consensus
is that they should be classified as algae, see discussion
below.)
As a result little attention has been paid to the numerous orders
of these microorganisms, and those studies that have been
conducted, have been predominantly carried out with a taxonomic or
ecological focus. For example, even though the simple fatty acid
distribution of several members of the order Thraustochytriales has
been reported from a taxonomic perspective (Ellenbogen, 1969);
Findlay et al.. 1986), no one has ever reported their total fatty
acid content or lipid content as percent dry weight. Unless data on
the total lipid content is available, one cannot evaluate an
organism's potential for use in the production of any type of fatty
acid. For example, the omega-3 highly unsaturated fatty acid
content of the lipids of some marine macroalgae (seaweeds) is
reported to be very high, up to 51% of total fatty acids (Pohl
& Zurheide, 1979). However, the lipid content of macroalgae is
typically very low, only 1-2% of cellular dry weight (Ryther,
1983). Therefore, despite the reported high content of omega-3
highly unsaturated fatty acids in the fatty acids of macroalgae,
they would be considered to be very poor candidate organisms for
the production of omega-3 highly unsaturated fatty acids. Despite a
diligent search by the inventor, no reports of simple proximate
analysis (% protein, carbohydrate and lipid) of the
Thraustochytriales has been found, nor has anyone reported attempts
to cultivate these species for purposes other than laboratory
studies of their taxonomy, physiology or ecology. Additionally,
many of the strains of these microorganisms have been isolated by
simple pollen baiting techniques (e.g., Gaertner, 1968). Pollen
baiting techniques are very specific for members of the
Thraustochytriales, but do not select for any characteristics which
may be desirable for large scale cultivation of microorganisms.
Thus, until the present invention, there have been no known
heterotrophic organisms suitable for culture that produce practical
levels of omega-3 highly unsaturated fatty acids and such organisms
have been thought to be very rare in the natural environment.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed toward a food product with a high
concentration of omega-3 highly unsaturated fatty acids (HUFAs)
which includes microorganisms characterized by having a high
concentration of fatty acids of which a high percentage are omega-3
highly unsaturated fatty acids. In addition or alternatively, the
food product can include omega-3 HUFAs extracted from the
microorganisms. Specifically, the microorganisms are
Thraustochytriales, namely, Thraustochytrium or Schizochytrium. The
microorganisms or extracted omega-3 HUFAs are incorporated with
additional food material which may be either animal food or human
food. The food product of the present invention may have the
bioavailability of the omega-3 HUFAs contained therein increased by
lysing the cells of the microorganisms. The food product may also
be extruded. In order to prevent degradation of the omega-3 HUFAs,
the food product may be packaged under non-oxidizing conditions or
may further comprise an antioxidant.
Another embodiment of the present invention relates to a method of
raising an animal comprising feeding the animal Thraustochytriales
or omega-3 HUFAs extracted therefrom. Animals raised by the method
of the present invention include poultry, cattle, swine and
seafood, which includes fish, shrimp and shellfish. The omega-3
HUFAs are incorporated into the flesh, eggs and other products of
these animals which are consumed by humans.
Omega-3 HUFAs may be consumed as the whole cell microbial product,
the extracted omega-3 HUFA product, or the animal or animal product
incorporating omega-3 HUFAs. Increased intake of omega-3 HUFAs
produced in accordance with the present invention by humans is
effective in preventing or treating cardiovascular diseases,
inflammatory and/or immunological diseases, and cancer.
Yet another embodiment of the present invention is a method of
producing omega-3 HUFAs which comprises culturing
Thraustochytriales in a medium with a source of organic carbon and
assimilable nitrogen. Preferably, the source of organic carbon and
assimilable nitrogen comprises ground grain. The method further
comprises culturing Thraustochytriales consisting of
Thraustochytrium, Schizochytrium, or mixtures thereof under
nutrient-limited or nitrogen-limited conditions for an effective
amount of time, preferably about 6 to about 24 hours, and
harvesting the Thraustochytriales during the period of nitrogen
limitation in order to increase the concentration of omega-3 HUFAs
in the microorganisms. The method further comprises adding an
antioxidant compound selected from the group consisting of BHT,
BHA, TBHQ, ethoxyquin, beta-carotene, vitamin E and vitamin C
during post-harvest processing in order to prevent degradation of
the omega-3 HUFAs. The method further comprises stressing the
microorganisms with low temperatures during culturing, maintaining
a high dissolved oxygen concentration in the medium during
culturing, and adding to the medium effective amounts of
phosphorous and a microbial growth factor (yeast extract or corn
steep liquor) to provide sustained growth of the microorganisms.
The present method further includes culturing unicellular
microorganisms having the identifying characteristics of ATCC Nos.
20888, 20889, 20890, 20891, 20892 and mutant strains derived
therefrom. Omega-3 HUFAs produced by the method can then be
separated from the lipids extracted from the microorganisms by
fractional crystallization which comprises rupturing the
microorganism cells, extracting the lipid mixture from the ruptured
cells with a solvent, hydrolyzing the lipid mixture, removing
non-saponifiable compounds and cold-crystallizing the non-HUFAs in
the lipid mixture.
A further embodiment of the present invention is a method for
selecting unicellular, aquatic microorganisms capable of
heterotrophic growth and capable of producing omega-3 HUFAs
comprising selecting microorganisms of a size between about 1 .mu.m
and 25 .mu.m from a small population of microorganisms collected
from naturally occuring shallow saline habitats, culturing the
microorganisms in a medium comprising organic carbon, assimilable
nitrogen, assimilable phosphorous and a microbial growth factor
under heterotrophic conditions, and selecting clear, white, orange,
or red-colored non-filamentous colonies having rough or textured
surfaces.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For purposes of definition throughout the application, it is
understood herein that a fatty acid is an aliphatic monocarboxylic
acid. Lipids are understood to be fats or oils including the
glyceride esters of fatty acids along with associated phosphatides,
sterols, alcohols, hydrocarbons, ketones, and related
compounds.
A commonly employed shorthand system is used in this specification
to denote the structure of the fatty acids (e.g., Weete, 1980).
This system uses the letter "C" accompanied by a number denoting
the number of carbons in the hydrocarbon chain, followed by a colon
and a number indicating the number of double bonds, i.e., C20:5,
eicosapentaenoic acid. Fatty acids are numbered starting at the
carboxy carbon. Position of the double bonds is indicated by adding
the Greek letter delta (.DELTA.) followed by the carbon number of
the double bond; i.e.. C20:5omega-3.DELTA..sup.5,8,11,14,17. The
"omega" notation is a shorthand system for unsaturated fatty acids
whereby numbering from the carboxy-terminal carbon is used. For
convenience, w3 will be used to symbolize "omega-3," especially
when using the numerical shorthand nomenclature described herein.
Omega-3 highly unsaturated fatty acids are understood to be
polyethylenic fatty acids in which the ultimate ethylenic bond is 3
carbons from and including the terminal methyl group of the fatty
acid. Thus, the complete nomenclature for eicosapentaenoic acid, an
omega-3 highly unsaturated fatty acid, would be
C20:5w3.DELTA..sup.5,8,11,14,17. For the sake of brevity, the
double bond locations (.DELTA..sup.5,8,11,14,17) will be omitted.
Eicosapentaenoic acid is then designated C20:5w3, Docosapentaenoic
acid (C22:5w3.DELTA..sup.7,10,13,16,19) is C22:5w3, and
Docosahexaenoic acid (C22:6w3.DELTA..sup.4,7,10,13,16,19) is
C22:6w3. The nonmenclature "highly unsaturated fatty acid" means a
fatty acid with 4 or more double bonds. "Saturated fatty acid"
means a fatty acid with 1 to 3 double bonds.
A collection and screening process was developed by the inventor to
readily isolate many strains of microorganisms with the following
combination of economically desirable characteristics for the
production of omega-3 highly unsaturated fatty acids: 1) capable of
heterotrophic growth; 2) high content of omega-3 highly unsaturated
fatty acids; 3) unicellular; 4) preferably low content of saturated
and omega-6 highly unsaturated fatty acids; 5) preferably
nonpigmented, white or essentially colorless cells; 6) preferably
thermotolerant (ability to grow at temperatures above 30.degree.
C.); and 7) preferably euryhaline (able to grow over a wide range
of salinities, but especially at low salinities).
Collection, isolation and selection of large numbers of suitable
heterotrophic strains can be accomplished by the following method.
Suitable water samples and organisms typically can be collected
from shallow, saline habitats which preferably undergo a wide range
of temperature and salinity variation. These habitats include
marine tide pools, estuaries and inland saline ponds, springs,
playas and lakes. Specific examples of these collection sites are:
1) saline warm springs such as those located along the Colorado
river in Glenwood Springs, Colo., or along the western edge of the
Stansbury Mountains, Utah; 2) playas such as Goshen playa located
near Goshen, Utah; 3) marine tide pools such as those located in
the Bird Rocks area of La Jolla, Calif.; and 4) estuaries, such as
Tiajuana estuary, San Diego County, Calif. Special effort should be
made to include some of the living plant matter and naturally
occurring detritus (decaying plant and animal matter) along with
the water sample. The sample can then be refrigerated until return
to the laboratory. Sampling error is minimized if the water sample
is shaken for 15-30 seconds, prior to pipetting or pouring a
portion, for example, 1-10 ml, into a filter unit. The filter unit
includes 2 types of filters: 1) on top, a sterile Whatman #4 filter
(Trademark, Whatman Inc., Clifton, N.J.); and 2) underneath the
Whatman filter, a polycarbonate filter with 1.0 .mu.m pore size.
The purpose of the first (top) filter is to remove all particulate
matter greater than about 25 .mu.m, generally allowing only
unicellular type material to pass onto the 1.0 .mu.m polycarbonate
filter. The first filter greatly reduces the number of mold
colonies that subsequently develop upon incubation of the
polycarbonate filter at elevated temperatures, thereby enhancing
the opportunities for other colonies to develop. Mold spores are
very numerous in coastal and inland saline waters, and mold
colonies can quickly cover an agar plate unless screened out. The
1.0 .mu.m size of the polycarbonate filter is chosen to allow many
of the bacteria to pass on through into the filtrate. The purpose
of using a sandwich filter design is to select for unicellular
organisms at least a portion of whose cells range in diameter from
about 1 .mu.m to about 25 .mu.m in size (organisms which could
potentially be grown easily in a fermenter system for production on
a large scale). Extensive growth of these unicellular organisms can
be encouraged by incubation of the polycarbonate filter on an agar
plate. Competition between organisms growing on the filter
facilitates the isolation of competitive, robust strains of
single-celled microorganisms. Unicellular aquatic microorganisms
selected by the foregoing method display a range of cell size
depending on growth conditions and stage of reproductive cycle.
Most cells in culture have diameters in the range from about 1
.mu.m to about 25 .mu.m; however, cells (thalli and sporangia) in
the cultures can be found that have larger diameters (depending on
the strain) up to about 60 .mu.m.
After filtration, the polycarbonate filter can be placed on an agar
plate containing saline media containing a source of organic carbon
such as carbohydrate including glucose, various starches, molasses,
ground corn and the like, a source of assimilable organic or
inorganic nitrogen such as nitrate, urea, ammonium salts, amino
acids, microbial growth factors included in one or more of yeast
extract, vitamins, and corn steep liquor, a source of assimilable
organic or inorganic phosphorous, and a pH buffer such as
bicarbonate. Microbial growth factors are currently unspecified
compounds which enhance heterotrophic growth of unicellular
microorganisms, including fungi and algae. The agar plates can be
incubated in the dark at 25.degree.-35.degree. C. (30.degree. C. is
preferred) and after 2-4 days numerous colonies will have appeared
on the filter. Recovery of 1-5 colonies/plate of the desired
organism is not uncommon. Yeast colonies are distinguishable either
by color (they frequently are pink) or by their morphology. Yeast
colonies are smooth whereas the desired organisms form in colonies
with rough or textured surfaces. Individual cells of the desired
organism can be seen through a dissecting microscope at the colony
borders, whereas yeast cells are not distinguishable, due to their
smaller size. Mold and higher fungi colonies are distinguishable
from the desired organisms because they are filamentous, whereas
the desired organisms are non-filamentous. Clear or white-colored
colonies can be picked from the plates and restreaked on a new
plate of similar media composition. While most of the desired
organisms are clear or white-colored, some are orange or
red-colored due to the presence of xanthophyll pigments and are
also suitable for selection and restreaking. The new plate can be
incubated under similar conditions, preferably at 30.degree. C. and
single colonies picked after a 2-4 day incubation period. Single
colonies can then be picked and placed in, for example, 50 ml of
liquid medium containing the same organic enrichments (minus agar)
as in the agar plates. These cultures can be incubated for 2-4 days
at 30.degree. C. with aeration, for example, on a rotary shaker
table (100-200 rpm.). When the cultures appear to reach maximal
density, 20-40 ml of the culture can then be harvested by
centrifugation or other suitable method and preserved, as by
lyophilization. The sample can then be analyzed by standard,
well-known techniques including gas chromatography techniques to
identify the fatty acid content of the strain. Those strains with
omega-3 highly unsaturated fatty acids can thereby be identified
and cultures of these strains maintained for further screening.
Promising strains can be screened for temperature tolerance by
inoculating the strains into 250 ml shaker flasks containing 50 ml
of culture media. These cultures are then incubated for 2 days on
the shaker table over any desired temperature range from most
practically between 27.degree.-48.degree. C., one culture at each
3.degree. C. interval. Production can be quantified as the total
amount of fatty acids produced per ml of culture medium. Total
fatty acids can be quantified by gas chromatography as described
above. A similar process can also be employed to screen for
salinity tolerance. For salinity tolerance a range of salinities
yielding conductivities from 5-40 mmho/cm is adequate for most
purposes. Screening for the ability to utilize a variety of carbon
and nitrogen sources can also be conducted employing the procedure
outlined above. The carbon and nitrogen sources were evaluated
herein at concentrations of 5 g/l. Carbon sources evaluated were:
glucose, corn starch, ground corn, potato starch, wheat starch, and
molasses. Nitrogen sources evaluated were: nitrate, urea, ammonium,
amino acids, protein hydrolysate, corn steep liquor, tryptone,
peptone, or casein. Other carbon and nitrogen sources can be used,
the choice being open to those of ordinary skill in the art, based
on criteria of significance to the user.
It has been unexpectedly found that species/strains from the genus
Thrausochytrium can directly ferment ground, unhydrolyzed grain to
produce omega-3 HUFAs. This process is advantageous over
conventional fermentation processes because such grains are
typically inexpensive sources of carbon and nitrogen. Moreover,
practice of this process has no detrimental effects on the
beneficial characteristics of the algae, such as levels of omega-3
HUFAs.
The present process using direct fermentation of grains is useful
for any type of grain, including without limitation, corn, sorghum,
rice, wheat, oats, rye and millet. There are no limitations on the
grind size of the grain. However, it is preferable to use at least
coarsely ground grain and more preferably, grain ground to a
flour-like consistency. This process further includes alternative
use of unhydrolyzed corn syrup or agricultural/fermentation
by-products such as stillage, a waste product in corn to alcohol
fermentations, as an inexpensive carbon/nitrogen source.
In another preferred process, it has been found that omega-3 HUFAs
can be produced by Thraustochytrium or Schizochytrium by
fermentation of above-described grains and waste products which
have been hydrolyzed. Such grains and waste products can be
hydrolyzed by any method known in the art, such as acid hydrolysis
or enzymatic hydrolysis. A further embodiment is a mixed hydrolysis
treatment. In this procedure, the ground grain is first partially
hydrolyzed under mild acid conditions according to any mild acid
treatment method known in the art. Subsequently, the partially
hydrolyzed ground grain is further hydrolyzed by an enzymatic
process according to any enzymatic process known in the art. In
this preferred process, enzymes such as amylase, amyloglucosidase,
alpha or beta glucosidase, or a mixture of these enzymes are used.
The resulting hydrolyzed product is then used as a carbon and
nitrogen source in the present invention.
Using the collection and screening process outlined above, strains
of unicellular fungi and algae can be isolated which have omega-3
highly unsaturated fatty acid contents up to 32% total cellular
ash-free dry weight (afdw), and which exhibit growth over a
temperature range from 15.degree.-48.degree. C. and grow in a very
low salinity culture medium. Many of the very high omega-3 strains
are very slow growers. Strains which have been isolated by the
method outlined above, and which exhibit rapid growth, good
production and high omega-3 highly unsaturated fatty acid content,
have omega-3 unsaturated fatty acid contents up to approximately
10% afdw.
Growth of the strains by the invention process can be effected at
any temperature conducive to satisfactory growth of the strains,
for example, between about 15.degree. C. and 48.degree. C., and
preferably between 25.degree.-36.degree. C. The culture medium
typically becomes more alkaline during the fermentation if pH is
not controlled by acid addition or buffers. The strains will grow
over a pH range from 4.0-11.0 with a preferable range of about
5.5-8.5.
When growth is carried out in large vessels and tanks, it is
preferable to produce a vegetative inoculum in a nutrient broth
culture by inoculating this broth culture with an aliquot from a
slant culture or culture preserved at -70.degree. C. employing the
cryoprotectants dimethylsulfoxide (DMSO) or glycerol. When a young,
active vegetative inoculum has then been secured, it can be
transferred aseptically to larger production tanks or fermenters.
The medium in which the vegetative inoculum is produced can be the
same as, or different from, that utilized for the large scale
production of cells, so long as a good growth of the strain is
obtained.
The inventor found that single-celled strains of the order
Thraustochytriales (containing omega-3 fatty acids) isolated and
screened by the process outlined above, generally exhibited
restricted growth, with vegetative growth terminating after a few
generations as predicted by Emerson (1950) and Schneider (1976).
However, the inventor found that by maintaining relatively high
concentrations of phosphorous (e.g., KH.sub.2 PO.sub.4 >0.2 g/l)
and/or adding a nutritional supplement (source of fungal growth
factors) such as yeast extract or corn steep liquor (greater than
0.2 g/l), continuously growing cultures of these unicellular fungi
could be maintained. The ability to maintain growth for more than
2-3 generations in liquid culture is termed herein sustained
growth. As a group, strains in the genus Thraustochytrium appear to
respond more favorably to phosphate additions than those in the
genus Schizochytrium, which appear to need less phosphate. In terms
of nutritional supplements supplying fungal growth factors, corn
steep liquor can be substituted for the yeast extract, and with
some strains, has even a more enhanced effect for allowing the
strains to achieve high densities in culture. The corn steep liquor
and yeast extract contain one or more growth factors necessary for
growth of the cells. While the growth factor(s) is not presently
defined, it is a component of yeast extract and corn steep liquor,
and either of these well-known nutritional supplements are
satisfactory. Carbon conversion efficiencies close to 50% (g cell
dry weight produced/100 g organic carbon added to culture medium)
can easily be achieved employing this process.
A microbial product high in protein and high in omega-3 highly
unsaturated fatty acids can be produced by harvesting the cells in
the exponential phase of growth. If a product significantly higher
in lipids and omega-3 highly unsaturated fatty acids is desired,
the culture can be manipulated to become nutrient limited,
preferably, nitrogen limited for a suitable time, preferably in the
range from 6 to 24 hours. The cultures can be transferred to a
nitrogen-free medium or, preferably, the initial nitrogen content
of the growth medium can be provided such that nitrogen becomes
depleted late in the exponential phase. Nitrogen limitation
stimulates total lipid production while maintaining high levels of
omega-3 highly unsaturated fatty acids as long as the induction
period is kept short, usually 6-24 hours. This phase of the
culture, when the culture population has achieved its maximum cell
density, is known as the stationary phase. Length of the induction
period can be manipulated by raising or lowering temperature,
depending on the strain employed. Additionally, the cells can be
cultured on a continuous basis in a medium with a high
carbon-to-nitrogen ratio, enabling continuous production of high
lipid content (and high omega-3 content) cellular biomass. The
unicellular strains of heterotrophic microorganisms isolated by the
screening procedure outlined above, tend to have high
concentrations of three omega-3 highly unsaturated fatty acids:
C20:5w3, C22:5w3 and C22:6w3 and very low concentration of C20:4w6.
The ratios of these fatty acids can vary depending on culture
conditions and the strains employed. Ratios of C20:5w3 to C22:6w3
can run from about 1:1 to 1:30. Ratios of C22:5w3 to C22:6w3 can
run from 1:12 to only trace amounts of C22:5w3. In the strains that
lack C22:5w3, the C20:5w3 to C 22:6w3 ratios can run from about 1:1
to 1:10. An additional highly unsaturated fatty acid, C22:5w6 is
produced by some of the strains, including all of the prior art
strains (up to a ratio of 1:4 with the C22:6w3 fatty acid).
However, C22:5w6 fatty acid is considered undesirable as a dietary
fatty acid because it can retroconvert to the C20:4w6 fatty acid.
The screening procedure outlined in this invention, however,
facilitates the isolation of some strains that contain no (or less
than 1%) omega-6 highly unsaturated fatty acids (C20:4w6 or
C22:5w6).
HUFAs in microbial products, such as those produced by the present
process, when exposed to oxidizing conditions can be converted to
less desirable unsaturated fatty acids or to saturated fatty acids.
However, saturation of omega-3 HUFAs can be reduced or prevented by
the introduction of synthetic antioxidants or naturally-occurring
antioxidants, such as betacarotene, vitamin E and vitamin C, into
the microbial products.
Synthetic antioxidants, such as BHT, BHA, TBHQ or ethoxyquin, or
natural antioxidants such as tocopherols, can be incorporated into
the food or feed products by adding them to the products during
processing of the cells after harvest. The amount of antioxidants
incorporated in this manner depends, for example, on subsequent use
requirements, such as product formulation, packaging methods, and
desired shelf life.
Concentrations of naturally-occurring antioxidants can be
manipulated by harvesting a fermentation in stationary phase rather
than during exponential growth, by stressing a fermentation with
low temperature, and/or by maintaining a high dissolved oxygen
concentration in the medium. Additionally, concentrations of
naturally occurring antioxidants can be controlled by varying
culture conditions such as temperature, salinity, and nutrient
concentrations. Additionally, biosynthetic precursors to vitamin E,
such as L-tyrosine or L-phenylalanine, can be incorporated into
fermentation medium for uptake and subsequent conversion to vitamin
E. Alternatively, compounds which act synergistically with
antioxidants to prevent oxidation (e.g., ascorbic acid, citric
acid, phosphoric acid) can be added to the fermentation for uptake
by the cells prior to harvest. Additionally, concentrations of
trace metals, particularly those that exist in two or more valency
states, and that possess suitable oxidation-reduction potential
(e.g., copper, iron, manganese, cobalt, nickel) should be
maintained at the minimum needed for optimum growth to minimize
their potential for causing autooxidation of the HUFAs in the
processed cells.
Other products that can be extracted from the harvested cellular
biomass include: protein, carbohydrate, sterols, carotenoids,
xanthophylls, and enzymes (e.g., proteases). Strains producing high
levels of omega-6 fatty acids have also been isolated. Such strains
are useful for producing omega-6 fatty acids which, in turn, are
useful starting materials for chemical synthesis of prostaglandins
and other eicosanoids. Strains producing more than 25% of total
fatty acids as omega-6 fatty acids have been isolated by the method
described herein.
The harvested biomass can be dried (e.g., spray drying, tunnel
drying, vacuum drying, or a similar process) and used as a feed or
food supplement for any animal whose meat or products are consumed
by humans. Similarly, extracted omega-3 HUFAs can be used as a feed
or food supplement. Alternatively, the harvested and washed biomass
can be used directly (without drying) as a feed supplement. To
extend its shelf life, the wet biomass can be acidified
(approximate pH 3.5-4.5) and/or pasteurized or flash heated to
inactivate enzymes and then canned, bottled or packaged under a
vacuum or non-oxidizing atmosphere (e.g., N.sub.2 or CO.sub.2) The
term "animal" means any organism belonging to the kingdom Animalia.
The term "animal" means any organism belonging to the kingdom
Animalia and includes, without limitation, any animal from which
poultry meat, seafood, beef, pork or lamb is derived. Seafood is
derived from, without limitation, fish, shrimp and shellfish. The
term "products" includes any product other than meat derived from
such animals, including, without limitation, eggs or other
products. When fed to such animals, omega-3 HUFAs in the harvested
biomass or extracted omega-3 HUFAs are incorporated into the flesh,
eggs or other products of such animals to increase the omega-3 HUFA
content thereof.
It should be noted that different animals have varying requirements
to achieve a desired omega-3 HUFA content. For example, ruminants
require some encapsulation technique for omega-3 HUFAs to protect
these unsaturated fatty acids from breakdown or saturation by the
rumen microflora prior to digestion and absorption of the omega-3
HUFAs by the animal. The omega-3 HUFA's can be "protected" by
coating the oils or cells with a protein (e.g., zeain) or other
substances which cannot be digested (or are poorly digested) in the
rumen. This allows the fatty acids to pass undamaged through the
ruminant's first stomach. The protein or other "protectant"
substance is dissolved in a solvent prior to coating the cells or
oil. The cells can be pelleted prior to coating with the
protectant. Animals having high feed conversion ratios (e.g.,
4:1-6:1) will require higher concentrations of omega-3 HUFAs to
achieved an equivalent incorporation of omega-3 HUFAs as animal
with low feed conversion ratios (2:1-3:1). Feeding techniques can
be further optimized with respect to the period of an animal's life
that harvested biomass or extracted omega-3 HUFAs must be fed to
achieve a desired result.
For most feed applications, the oil content of the harvested cells
will be approximately 25-50% afdw, the remaining material being
protein and carbohydrate. The protein can contribute significantly
to the nutritional value of the cells as several of the strains
that have been evaluated have all of the essential amino acids and
would be considered a nutritionally balanced protein.
In a preferred process, the freshly harvested and washed cells
(harvested by belt filtration, rotary drum filtration,
centrifugation, etc.) containing omega-3 HUFAs can be mixed with
any dry ground grain in order to lower the water content of the
harvested cell paste to below 40% moisture. For example, corn can
be used and such mixing will allow the cell paste/corn mixture to
be directly extruded, using common extrusion procedures. The
extrusion temperatures and pressures can be modified to vary the
degree of cell rupture in the extruded product (from all whole
cells to 100% broken cells). Extrusion of the cells in this manner
does not appear to greatly reduce the omega-3 HUFA content of the
cells, as some of the antioxidants in the grain may help protect
the fatty acids from oxidation, and the extruded matrix may also
help prevent oxygen from readily reaching the fatty acids.
Synthetic or natural antioxidants can also be added to the cell
paste/grain mixture prior to extrusion. By directly extruding the
cell paste/grain mixture, drying times and costs can be greatly
reduced, and it allows manipulation of the bioavailability of the
omega-3 HUFAs for feed supplement applications by degree of cell
rupture. The desired degree of cell rupture will depend on various
factors, including the acceptable level of oxidation (increased
cell rupture increases likelihood of oxidation) and the required
degree of bioavailability by the animal consuming the extruded
material.
The unicellular fungal strains isolated by the method described
readily flocculate and settle, and this process can be enhanced by
adjusting the pH of the culture to pH .ltoreq.7.0. A 6-fold
concentration of the cells within 1-2 minutes can be facilitated by
this process. The method can therefore be employed to
preconcentrate the cells prior to harvesting, or to concentrate the
cells to a very high density prior to nitrogen limitation. Nitrogen
limitation (to induce higher lipid production) can therefore be
carried out in a much smaller reactor, or the cells from several
reactors consolidated into one reactor.
A variety of procedures can be employed in the recovery of the
microbial cells from the culture medium. In a preferred recovery
process, the cells produced by the subject process are recovered
from the culture medium by separation by conventional means, such
as by filtration or centrifugation. The cells can then be washed;
frozen, lyophilized, or spray dried; and stored under a
non-oxidizing atmosphere of a gas such as CO.sub.2 or N.sub.2 (to
eliminate the presence of O.sub.2), prior to incorporation into a
processed food or feed product.
Cellular lipids containing the omega-3 highly unsaturated fatty
acids can also be extracted from the microbial cells by any
suitable means, such as by supercritical fluid extraction, or by
extraction with solvents such as chloroform, hexane, methylene
chloride, methanol, and the like, and the extract evaporated under
reduced pressure to produce a sample of concentrated lipid
material. The omega-3 highly unsaturated fatty acids in this
preparation may be further concentrated by hydrolyzing the lipids
and concentrating the highly unsaturated fraction by employing
traditional methods such as urea adduction or fractional
distillation (Schlenk, 1954), column chromatography (Kates, 1986),
or by supercritical fluid fractionation (Hunter, 1987). The cells
can also be broken or lysed and the lipids extracted into vegetable
or other edible oil (Borowitzka and Borowitzka, 1988). The
extracted oils can be refined by well-known processes routinely
employed to refine vegetables oils (e.g. chemical refining or
physical refining). These refining processes remove impurities from
extracted oils before they are used or sold as edible oils. The
refining process consists of a series of processes to degum,
bleach, filter, deodorize and polish the extracted oils. After
refining, the oils can be used directly as a feed or food additive
to produce omega-3 HUFA enriched products. Alternatively, the oil
can be further processed and purified as outlined below and then
used in the above applications and also in pharmaceutical
applications.
In a preferred process, a mixture of high purity omega-3 HUFAs or
high purity HUFAs can be easily concentrated from the extracted
oils. The harvested cells (fresh or dried) can be ruptured or
permeabilized by well-known techniques such as sonication,
liquid-shear disruption methods (e.g., French press of
Manton-Gaulin homogenizer), bead milling, pressing under high
pressure, freeze-thawing, freeze pressing, or enzymatic digestion
of the cell wall. The lipids from the ruptured cells are extracted
by use of a solvent or mixture of solvents such as hexane,
chloroform, ether, or methanol. The solvent is removed (for example
by a vacuum rotary evaporator, which allows the solvent to be
recovered and reused) and the lipids hydrolyzed by using any of the
well-known methods for converting triglycerides to free fatty acids
or esters of fatty acids including base hydrolysis, acid
hydrolysis, or enzymatic hydrolysis. The hydrolysis should be
carried out at as low a temperature as possible (e.g., room
temperature to 60.degree. C.) and under nitrogen to minimize
breakdown of the omega-3 HUFAs. After hydrolysis is completed, the
nonsaponifiable compounds are extraced into a solvent such as
ether, hexane or chloroform and removed. The remaining solution is
then acidified by addition of an acid such as HCl, and the free
fatty acids extracted into a solvent such as hexane, ether, or
chloroform. The solvent solution containing the free fatty acids
can then be cooled to a temperature low enough for the non-HUFAs to
crystallize, but not so low that HUFAs crystallize. Typically, the
solution is cooled to between about -60.degree. C. and about
-74.degree. C. The crystallized fatty acids (saturated fatty acids,
and mono-, di-, and tri-enoic fatty acids) can then be removed
(while keeping the solution cooled) by filtration, centrifugation
or settling. The HUFAs remain dissolved in the filtrate (or
supernatant). The solvent in the filtrate (or supernatant) can then
be removed leaving a mixture of fatty acids which are >90%
purity in either omega-3 HUFAs or HUFAs which are greater than or
equal to 20 carbons in length. The purified omega-3 highly
unsaturated fatty acids can then be used as a nutritional
supplement for humans, as a food additive, or for pharmaceutical
applications. For these uses the purified fatty acids can be
encapsulated or used directly. Antioxidants can be added to the
fatty acids to improve their stability.
The advantage of this process is that it is not necessary to go
through the urea complex process or other expensive extraction
methods, such as supercritical CO.sub.2 extraction or high
performance liquid chromatography, to remove saturated and
mono-unsaturated fatty acids prior to cold crystallization. This
advantage is enabled by starting the purification process with an
oil consisting of a simple fatty acid profile such as that produced
by Thraustochytrids (3 or 4 saturated or monounsaturated fatty
acids with 3 or 4 HUFAs, two groups of fatty acids widely separated
in terms of their crystallization temperatures) rather than a
complex oil such as fish oil with up to 20 fatty acids
(representing a continuous range of saturated, mono-, di-, tri-,
and polyenoic fatty acids, and as such, a series of overlapping
crystallization temperatures).
In a preferred process, the omega-3 HUFA enriched oils can be
produced through cultivation of strains of the genus
Thraustochytrium. After the oils are extracted from the cells by
any of several well-known methods, the remaining extracted (lipids
removed) biomass which is comprised mainly of proteins and
carbohydrates, can be sterilized and returned to the fermenter,
where the strains of Thraustochytrium can directly recycle it as a
nutrient source (source of carbon and nitrogen). No prehydrolysis
or predigestion of the cellular biomass is necessary. Extracted
biomass of the genus Schizochytrium can be recycled in a similar
manner if it is first digested by an acid and/or enzymatic
treatment.
As discussed in detail above, the whole-cell biomass can be used
directly as a food additive to enhance the omega-3 highly
unsaturated fatty acid content and nutritional value of processed
foods for human intake or for animal feed. When used as animal
feed, omega-3 HUFAs are incorporated into the flesh or other
products of animals. The complex lipids containing these fatty
acids can also be extracted from the whole-cell product with
solvents and utilized in a more concentrated form (e.g.,
encapsulated) for pharmaceutical or nutritional purposes and
industrial applications. A further aspect of the present invention
includes introducing omega-3 HUFAs from the foregoing sources into
humans for the treatment of various diseases. As defined herein,
"treat" means both the remedial and preventative practice of
medicine. The dietary value of omega-3 HUFAs is widely recognized
in the literature, and intake of omega-3 HUFAs produced in
accordance with the present invention by humans is effective for
treating cardiovascular diseases, inflammatory and/or immunological
diseases and cancer.
The present invention will be described in more detail by way of
working examples. Species meeting the selection criteria described
above have not been described in the prior art. By employing these
selection criteria, the inventor isolated over 25 potentially
promising strains from approximately 1000 samples screened. Out of
the approximate 20,500 strains in the American Type Culture
Collection (ATCC), 10 strains were later identified as belonging to
the same taxonomic group as the strains isolated by the inventor.
Those strains still viable in the Collection were procured and used
to compare with strains isolated and cultured by the disclosed
procedures. The results of this comparison are presented in
Examples 5 and 6 below.
Since the filing of the parent case, recent developments have
resulted in revision of the taxonomy of the Thraustochytrids. The
most recent taxonomic theorists place them with the algae. However,
because of the continued taxonomic uncertainty, it would be best
for the purposes of the present invention to consider the strains
as Thraustochydrids (Order: Thraustochytriales; Family:
Thraustochytriaceae; Genus: Thraustochytrium or Schizochytrium).
The most recent taxonomic changes are summarized below.
All of the strains of unicellular microorganisms disclosed and
claimed herein are members of the order Thraustochytriales.
Thraustochytrids are marine eukaryotes with a rocky taxonomic
history. Problems with the taxonomic placement of the
Thraustochytrids have been reviewed most recent by Moss (1986),
Bahnweb and Jackle (1986) and Chamberlain and Moss (1988). For
convenience purposes, the Thraustochytrids were first placed by
taxonomists with other colorless zoosporic eukaryotes in the
Phycomycetes (algae-like fungi). The name Phycomycetes, however,
was eventually dropped from taxonomic status, and the
Thraustochytrids retained in the Oomycetes (the biflagellate
zoosporic fungi). It was initially assumed that the Oomycetes were
related to the heterokont algae, and eventually a wide range of
ultrastructural and biochemical studies, summarized by Barr (1983)
supported this assumption. The Oomycetes were in fact accepted by
Leedale (1974) and other phycologists as part of the heterokont
algae. However, as a matter of convenience resulting from their
heterotrophic nature, the Oomycetes and Thraustochytrids have been
largely studied by mycologists (scientists who study fungi) rather
than phycologists (scientists who study algae).
From another taxonomic perspective, evolutionary biologists have
developed two general schools of thought as to how eukaryotes
evolved. One theory proposes an exogenous origin of membrane-bound
organelles through a series of endosymbioses (Margulis (1970);
e.g., mitochondria were derived from bacterial endosymbionts,
chloroplasts from cyanophytes, and flagella from spirochaetes). The
other theory suggests a gradual evolution of the membrane-bound
organelles from the non-membrane-bounded systems of the prokaryote
ancestor via an autogenous process (Cavalier-Smith 1975). Both
groups of evolutionary biologists however, have removed the
Oomycetes and Thraustachytrids from the fungi and place them either
with the chromophyte algae in the kingdom Chromophyta
(Cavalier-Smith 1981) or with all algae in the kingdom Protoctista
(Margulis and Sagan (1985).
With the development of electron microscopy, studies on the
ultrastructure of the zoospores of two genera of Thraustochytrids,
Thraustochytrium and Schizochytrium. (Perkins 1976; Kazama 1980;
Barr 1981) have provided good evidence that the Thraustochytriaceae
are only distantly related to the Oomycetes. Additionally, more
recent genetic data representing a correspondence analysis (a form
of multivariate statistics) of 5S ribosomal RNA sequences indicate
that Thraustochytriales are clearly a unique group of eukaryotes,
completely separate from the fungi, and most closely related to the
red and brown algae, and to members of the Oomycetes (Mannella et
al. 1987). Recently however, most taxonomists have agreed to remove
the Thraustochytrids from the Oomycetes (Bartnicki-Garcia
1988).
In summary, employing the taxonomic system of Cavalier-Smith (1981,
1983), the Thraustochytrids are classified with the chromophyte
algae in the kingdom Chromophyta, one of the four plant kingdoms.
This places them in a completely different kingdom from the fungi,
which are all placed in the kingdom Eufungi. The taxonomic
placement of the Thraustochytrids is therefore summarized
below:
Kingdom: Chromophyta
Phylum: Heterokonta
Order: Thraustochytriales
Family: Thraustochytriaceae
Genus: Thraustochytrium or Schizochytrium
Despite the uncertainty of taxonomic placement within higher
classifications of Phylum and Kingdom, the Thraustochytrids remain
a distinctive and characteristic grouping whose members remain
classifiable within the order Thraustochytriales.
Omega-3 highly unsaturated fatty acids are nutritionally important
fatty acids for both humans and animals. Currently the only
commercially available source of these fatty acids is from fish
oil. However, there are several significant problems with the use
of fish oil as a food or feed additive or supplement. First and
most significantly, fish oils have a strong fishy taste and odor,
and as such cannot be added to processed foods as a food additive,
without negatively affecting the taste of the food product. This is
also true for many of its applications as an animal food or feed
additive. For example, experiments by the inventor and others have
indicated that laying hens readily go off their feed when fed for
more than a few days on feed enriched with fish oils. Fish oils are
very unstable, easily becoming rancid and thereby decreasing the
palatability and nutritional value of feed.
Secondly, fish oils generally only contain 20-30% omega-3 HUFAs.
Desirable omega-3 HUFA contents in marine larval fish and shrimp
feeds can be as high as 5-10% of their dry weight. To constitute an
appropriate synthetic diet containing 5-10% omega-3 HUFAs could
require a diet of 15-30% fish oil. Such a synthetic diet would not
be the most suitable for these larval organisms either in terms of
palatability, digestibility, or stability (Sargent et al. (1989).
In terms of human nutrition, the other 70-80% of fatty acids in
fish oil are saturated and omega-6 fatty acids, fatty acids which
can have deleterious health effects for humans. Processes for the
isolation of pure omega-3 fatty acids from fish oils are involved
and expensive, resulting in very high prices ($200-$1000/ g) for
pure forms of these fatty acids, much too expensive for use as a
food or feed additive (Sigma Chemical, Co., 1988; CalBiochem Co.,
1988).
Third, most feeds currently used by the aquaculture industry are
grain based feeds, and as such, are relatively low in omega-3 HUFA
content. Recent surveys of seafood products have demonstrated that
fish and shrimp produced by aquaculture farms generally only have
1/3-1/2 the omega-3 HUFA content of wild caught fish and shrimp
(Pigott 1989). For aquacultured organisms, many which are prized
because of their mild, non-fishy taste, increasing the fish oil
content of their food is not effective, because it results in a
fish-tasting product.
As a result of the problems described above, there is an important
need for development of alternative (non-fish based) sources of
omega-3 HUFAs.
The microbial product of the present invention can be used as a
food or feed supplement to provide an improved source of omega-3
highly unsaturated fatty acids which has significant advantages
over conventional sources. Poultry fed a diet supplemented with the
microbial product incorporate the omega-3 highly unsaturated fatty
acids into body tissues and into eggs. The eggs exhibit no fishy
odor or taste, no change in yolk color. The poultry do not stop
eating the supplemented feed, as they do with fish oil-supplemented
feed. Feed supplemented with the microbial product of the present
invention has a normal shelf life and does not become rancid upon
standing at room temperature for several days. The eggs and flesh
of poultry fed according to the invention are useful in human
nutrition as sources of omega-3 highly unsaturated fatty acids, yet
are low in omega-6 fatty acid content and lack a fishy flavor.
The microbial product of the present invention is also of value as
a source of omega-3 highly unsaturated fatty acids for fish, shrimp
and other products produced by aquaculture. The product can be
added directly as a supplement to the feed or it can be fed to
brine shrimp or other live feed organisms intended for consumption
by the aquacultured product. The use of such supplement enables the
fish or shrimp farmer to bring to market an improved product
retaining the taste advantages provided by aquaculture but having
the high omega-3 highly unsaturated fatty acid content of wild
caught fish coupled to the additional health advantage of reduced
omega-6 fatty acid content.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a bar graph showing the effects of various media
supplements on fatty acid yield, using Thraustochytrium sp. UT42-2
(ATCC No. 20891), a strain isolated according to the selection
method of the invention as a test strain. The experimental
procedure is described in Example 2. Ordinate: fatty acid yield,
normalized to control, FFM media without supplements. Abscissa:
specific additions, 1) 2x "B"-vitamin mix; 2) "A" vitamin mix; 3)
2x PI metals; 4) 28 mg/1 KH.sub.2 PO.sub.4 ; 5) treatments 2), 3)
and 4) combined; and 6) 480 mg/1 KH.sub.2 PO.sub.4.
FIG. 2 is a graphical representation of highly unsaturated fatty
acid production in newly isolated strains of the invention,
represented by .quadrature. and previously isolated strains
represented by +. Each point represents a strain, the position of
each point is determined by the percent by weight of total fatty
acids which were omega-3 highly unsaturated fatty acids (abscissa)
and the percent by weight of total fatty acids which were omega-6
fatty acids (ordinate). Only those strains of the invention were
plotted wherein less than 10.6% (w/w) of total fatty acids were
omega-6 and more than 67% of total fatty acids were omega-3. Data
from Table 4.
FIG. 3 is a graphical representation of highly unsaturated fatty
acid production in newly isolated strains of the invention,
represented by .quadrature. and previously isolated strains,
represented by +. Each point represents a strain, the position of
each point is determined by the percent by weight of total fatty
acids which were omega-3 highly unsaturated fatty acids (abscissa)
and percent of weight of total fatty acids which were
eicosapentaenoic acid (EPA C20:5w3) (ordinate). Only those strains
of the invention were plotted wherein more than 67% (w/w) of total
fatty acids were omega-3 and more than 7.8% (w/w) of total fatty
acids were C20:5w3.
FIG. 4 is a graphical representation of omega-3 highly unsaturated
fatty acid composition in newly isolated strains of the invention,
represented by .quadrature., and previously isolated strains,
represented by +. Each point represents a separate strain. Values
on the abscissa are weight fraction of total omega-3 highly
unsaturated fatty acids which were C20:5w3 and on the ordinate are
weight fraction of total omega-3 fatty highly unsaturated acids
which were C22:6w3. Only strains of the invention were plotted
having either a weight fraction of C20:5w3 28% or greater, or a
weight fraction of C22:6w3 greater than 93.6%.
FIG. 5 is a graph showing growth of various newly isolated strains
of the invention and previously isolated strains, at 25.degree. C.
and at 30.degree. C. Growth rates are normalized to the growth rate
of strain U-30 at 25.degree. C. Previously isolated strains are
designated by their ATCC accession numbers. Numerical data in terms
of cell number doublings per day are given in Table 5.
FIG. 6 is a graph of total yields of cellular production after
induction by nitrogen limitation. Each of ash-free dry weight,
total fatty acids and omega-3 highly unsaturated fatty acids, as
indicated, was plotted, normalized to the corresponding value for
strain 28211. All strains are identified by ATCC accession
numbers.
FIG. 7 is a graph of fatty acid yields after growth in culture
media having the salinity indicated on the abscissa. Strains shown
are newly isolated strains S31 (ATCC 20888) (.quadrature.) and
U42-2 (ATCC 20891) (+) and previously isolated strains, ATCC 28211
and ATCC 28209 (.DELTA.). Fatty acid yields are plotted was
relative yields normalized to an arbitrary value of 1.00 based on
the average growth rate exhibited by S31 (ATCC 20888)
(.quadrature.) over the tested salinity range.
FIG. 8 is a graph of increases in the omega-3 highly unsaturated
fatty acid content of the total lipids in the brine shrimp, Artemia
salina, fed Thraustochytrid strain (ATCC 20890) isolated by the
method in Example 1. EPA =C20:5w3; DHA =C22:6w3.
FIG. 9 is a graph of increases in the omega-3 highly unsaturated
fatty acid content of the total lipids in the brine shrimp, Artemia
salina, fed Thraustochytrid strain (ATCC 20888) isolated by the
method in Example 1. EPA =C20:5w3; DHA =C22:6w3.
EXAMPLES
Example 1. Collection and Screening
A 150 ml water sample was collected from a shallow, inland saline
pond and stored in a sterile polyethylene bottle. Special effort
was made to include some of the living plant material and naturally
occurring detritus (decaying plant and animal matter) along with
the water sample. The sample was placed on ice until return to the
laboratory. In the lab, the water sample was shaken for 15-30
seconds, and 1-10 ml of the sample was pipetted or poured into a
filter unit containing 2 types of filters: 1) on top, a sterile 47
mm diameter Whatman #4 filter having a pore size about 25 .mu.m;
and 2) underneath the Whatman filter, a 47 mm diameter
polycarbonate filter with about 1.0 .mu.m pore size. Given slight
variations of nominal pore sizes for the filters, the cells
collected on the polycarbonate filter range in size from about 1.0
.mu.m to about 25 .mu.m.
The Whatman filter was removed and discarded. The polycarbonate
filter was placed on solid F-1 media in a petri plate, said media
consisting of (per liter): 600 ml seawater (artificial seawater can
be used), 400 ml distilled water, 10 g agar, 1 g glucose, 1 g
protein hydrolysate, 0.2 g yeast extract, 2 ml 0.1 M KH.sub.2
PO.sub.4, 1 ml of a vitamin solution (A-vits) (Containing 100 mg/l
thiamine, 0.5 mg/l biotin, and 0.5 mg/l cyanocobalamin), b 5 ml of
a trace metal mixture (PII metals, containing per liter: 6.0 g
Na.sub.2 EDTA, 0.29 g FeCl.sub.3 6H.sub.2 O, 6.84 g H.sub.3
BO.sub.3, 0.86 MnCl.sub.2 4H.sub.2 O, 0.06 g ZnCl.sub.2, 0.026 g
CoCl.sub.2 6H.sub.2 O, (0.052 g NiSO.sub.4 H=hd 2O, 0.002 g
CuSo.sub.4 5H.sub.2 O, and 0.005 g Na.sub.2 MoO.sub.4 2H.sub.2 O,
and 500 mg each of streptomycin sulfate and peniocillin-G. The agar
plate was incubated in the dark at 30.degree. C. After 2-4 days
numerous colonies appeared on the filter. Colonies of unicellular
fungi (except yeast) were picked from the plate and restreaked on a
new plate of similar media composition. Special attention was made
to pick all colonies consisting of colorless or white cells. The
new plate was incubated at 30.degree. C. and single colonies picked
after a 2-4 day incubation period. Single colonies were then picked
and placed in 50 ml of liquid medium containing the same organic
enrichments as in the agar plates. These cultures were incubated
for 2.gtoreq.4 days at 30.degree. C. on a rotary shaker table
(100-200 rpm). When the cultures appeared to reach maximal density,
20-40 ml of the culture was harvested, centrifuged and lyphilized.
The sample was then analyzed by standard, well-known gas
chromatographic techniques (e.g., Lepage and Roy, 1984) to identify
the fatty acid content of the strain. Those strains with omega-3
highly unsaturated fatty acids were thereby identified, and
cultures of these strains were maintained for further
screening.
Using the collection and screening process outlined above, over 150
strains of unicellular fungi have been isolated which have omega-3
highly unsaturated fatty acid contents up to 32% total cellular
ash-free dry weight, and which exhibit growth over a temperature
range from 15-48.degree. C. Strains can also be isolated which have
less than 1% (as % of total fatty acids) of the undesirable C20:4w6
and C22:5w6 highly unsaturated fatty acids. Strains of these fungi
can be repeatedly isolated from the same location using the
procedure outlined above. A few of the newly isolated strains have
very similar fatty acid profiles. The possibility that some are
duplicate isolates of the same strain cannot be ruled out at
present. Further screening for other desirable traits such as
salinity tolerance or ability to use a variety of carbon and
nitrogen sources can then be carried out using a similar
process.
Example 2. Maintaining unrestricted cell growth: phosphorus
Cells of Thraustochytrium sp. U42-2 (ATCC No. 20891), a strain
isolated by the method in Example 1, were picked from solid
F-medium and inoculated into 50 ml of modified FFM medium (Fuller
et al., 1964). This medium containing: seawater, 1000 ml; glucose,
1.0 g; gelatin hydrolysate, 1.0 g; liver extract, 0.01 g; yeast
extract, 0.1 g; PII metals, 5 ml; 1 ml B-vitamins solution
(Goldstein et al., 1969); and 1 ml of an antibiotic solution (25
g/l streptomycin sulfate and penicillin-G). 1.0 ml of the vitamin
mix (pH 7.2) contains: thiamine HC1, 200 .mu.g; biotin, 0.5 .mu.g;
cyanocobalamin, 0.05 .mu.g; nicotinic acid, 100 .mu.g; calcium
pantothenate, 100 .mu.g; riboflavin, 5.0 .mu.g; pyridoxine HC1,
40.0 .mu.g; pyridoxamine 2HC1, 10.0 .mu.g; p-aminobenzoic acid, 10
.mu.g; chlorine HC1, 500 .mu.g; inositol, 1.0 mg; thymine, 0.8 mg;
orotic acid, 0.26 mg; folinic acid, 0.2 .mu.g; and folic acid, 2.5
.mu.g. 250 ml erlenmeyer flasks with 50 ml of this medium were
placed on an orbital shaker (200 rpm) at 27.degree. C. for 2-4
days, at which time the culture had reached their highest
densities. One ml of this culture was transferred to a new flask of
modified FFM medium, with the extra addition of one of the
following treatments on a per liter basis: 1) 1 ml of the B-vitamin
mix; 2) 1 ml of A-vitamin solution; 3) 5 ml PII Metals; 4) 2 ml of
0.1 M KH.sub.2 PO.sub.2 (.apprxeq.28 mg); 5) treatments 2, 3, and 4
combined; and 6) 480 mg KH.sub.2 PO.sub.4. One ml of the culture
was also transferred to a flask of modified FFM medium which had no
extra additions made to it and served as a control for the
experiment. The cultures were incubated for 48 hr. at 27.degree. C.
on a rotary shaker (200 rpm). The cells were then harvested by
centrifugation and the fatty acids were quantified by gas
chromatography. The results are illustrated in FIG. 1 and Table 1.
In FIG. 1, the yields are plotted as ratios of the control, whose
relative yield is therefore 1.0. Treatments 1-6 are as follows: 1)
2x concentration of B vitamins; 2) 2x concentration of A vitamins;
3) 2x concentration of trace metals; 4) 2x concentration of (B
vitamins+phosphate+trace metals); 5) 2x concentration of phosphate;
and 6) 24 mg phosphate per 50 ml (0.48 g per liter). Only the
treatment of adding 0.48 g KH.sub.2 OP.sub.4 per liter resulted in
enhanced growth and resulted in significantly increased fatty acid
yield.
TABLE 1 ______________________________________ Effect of various
nutrient additions on the yield of fatty acids in Thraustochytrium
sp. U42-2 (ATCC No. 20891) Fatty Acid Yield Treatment mg/liter
______________________________________ Control 23 2 .times.
concentration of B vitamin mix 17 2 .times. concentration of A
vitamin mix 24 2 .times. concentration trace metals 27 2 .times.
concentration B vitamin mix, 24 2 .times. PO.sub.4 and 2 .times.
concentration trace metals 2 .times. concentration PO.sub.4 23 24
mg phosphate per 50 ml 45
______________________________________
Example 3. Maintaining unrestricted growth: PO.sub.4 and yeast
extract
Cells of Schizochytrium aggregatum (ATCC 28209) were picked from
solid F-1 medium and inoculated into 50 ml of FFM medium. The
culture was placed on a rotary shaker (200 rpm) at 27.degree. C.
After 3-4 days, 1 ml of this culture was transferred to 50 ml of
each of the following treatments: 1) FFM medium (as control); and
2) FFM medium with the addition of 250 mg/1 KH2PO.sub.4 and 250
mg/1 yeast extract. These cultures were placed on a rotary shaker
(200 rpm) at 27.degree. C. for 48 hr. The cells were harvested and
the yield of cells quantified. In treatment 1, the final
concentration of cells on an ash-free dry weight basis was 616
mg/l. In treatment 2, the final concentration of cells was 1675
mg/l, demonstrating the enhanced effect of increasing PO.sub.4 and
yeast extract concentrations in the culture medium.
Example 4. Maintaining unrestricted growth: substitution of corn
steep liquor for yeast extract
Cells of Schizochytrium sp. S31 (ATCC No. 20888) were picked from
solid F-1 medium and placed into 50 ml of M-5 medium. This medium
consists of (on a per liter basis): NaCl, 25 g; MgSO.sub.4.7H.sub.2
O, 5 g; KCl, 1 g; CaCl.sub.2, 200 mg; glucose, 5 g; glutamate, 5 g;
KH.sub.2 PO.sub.4, 1 g; PII metals, 5 ml; A-vitamins solution, 1
ml; and antibiotic solution, 1 ml. The pH of the solution was
adjusted to 7.0 and the solution was filter sterilized. Sterile
solutions of corn steep liquor (4 g/40 ml; pH 7.0) and yeast
extract 1 g/40 ml; pH 7.0) were prepared. To one set of M-5 medium
flasks, the following amount of yeast extract solution was added:
1) 2 ml; 2) 1.5 ml; 3) 1 ml; 4) 0.5 ml; and 5) 0.25 ml. To another
set of M-5 medium flasks the yeast extract and corn steep liquor
solutions were added at the following levels: 1) 2 ml yeast
extract; 2) 1.5 ml yeast extract and 0.5 ml corn steep liquor; 3)
1.0 ml yeast extract and 1.0 ml corn steep liquor; 4) 0.5 ml yeast
extract and 1.5 ml corn steep liquor; and 5) 2 ml corn steep
liquor. One ml of the culture in F-1 medium was used to inoculate
each flask. They were placed on a rotary shaker at 27.degree. C.
for 48 hr. The cells were harvested by centrifugation and the yield
of cells (as ash-free dry weight) was determined. The results are
shown in Table 2. The results indicate the addition of yeast
extract up to 0.8 g/1 of medium can increase the yield of cells.
However, addition of corn steep liquor is even more effective and
results in twice the yield of treatments with added yeast extract.
This is very advantageous for the economic production of cells as
corn steep liquor is much less expensive than yeast extract.
TABLE 2 ______________________________________ Treatment (Amount
Nutrient Ash-Free Dry Weight Supplement Added) (mg/l)
______________________________________ 2.0 ml yeast ext. 4000 1.5
ml yeast ext. 4420 1.0 ml yeast ext. 4300 0.5 ml yeast ext. 2780
0.25 ml yeast ext. 2700 2.0 ml yeast ext. 4420 1.5 ml yeast ext. +
0.5 ml CSL* 6560 1.0 ml yeast ext. + 1.0 ml CSL 6640 0.5 ml yeast
ext. + 1.5 ml CSL 7200 2.0 ml CSL 7590
______________________________________ *CSL = corn steep liquor
Example 5. Enhanced highly unsaturated fatty acid content of
strains isolated by method in Example 1 compared to ATCC strains
(previously known strains)
A battery of 151 newly isolated strains, selected according to the
method described in Example 1, were sampled in late exponential
phase growth and quantitatively analyzed for highly unsaturated
fatty acid content by gas-liquid chromatography. All strains were
grown either in Ml medium or liquid FFM medium, whichever gave
highest yield of cells. Additionally, five previously isolated
Thraustochytrium or Schizochytrium species were obtained from the
American Type Culture Collection, representing all the strains
which could be obtained in viable form from the collection. These
strains were: T. aureum (ATCC No. 8211), T. aureum (ATCC No.
34304), T. roseum (ATCC No. 8210), T. straitum (ATCC No. 34473) and
S. aggregatum (ATCC No. 28209). The strains all exhibited
abbreviated growth in conventional media, and generally showed
improved growth in media of the present invention, including M5
medium and FFM medium, Example 2. The fatty acids production of
each of the known strains was measured as described, based upon the
improved growth of the strains in media of the invention.
Fatty acid peaks were identified by the use of pure compounds of
known structure. Quantitation, in terms of percent by weight of
total fatty acids, was carried out by integrating the
chromatographic peaks. Compounds identified were: palmitic acid
(C16:0), C20:4w6 and C22:1 (which were not resolved separately by
the system employed), C20:5w3, C22:5w6, C22:5w3, and C22:6w3. The
remainder, usually lower molecular weight fatty acids, were
included in the combined category of "other fatty acids." Total
omega-3 fatty acids were calculated as the sum of 20:5w3, 22:5w3
and 22:6w3. Total omega-6 fatty acids were calculated as the sum of
the 20:4/22:1 peak and the 22:5w6 peak.
The results are shown in Tables 3-4 and illustrated in FIGS. 2-4.
From Table 3 it can be seen that large numbers of strains can be
isolated by the method of the invention, and that large numbers of
strains outperform the previously known strains by several
important criteria. For example, 102 strains produced at least 7.8%
by weight of total fatty acids C20:5w3, a higher percentage of that
fatty acid than any previously known strain. Strains 23B (ATCC No.
20892) and 12B (ATCC No. 20890) are examples of such strains.
Thirty (30) strains of the invention produced at least 68% by
weight of total fatty acids as omega-3 fatty acids, more than any
previously known strain. Strain 23B (ATCC No. 20892) is an example
of such strains. Seventy-six (76) strains of the invention yielded
not more than 10% by weight of total fatty acids as omega-6 fatty
acids, considered undesirable components of the human diet, lower
than any previously known strain. Strains 23B (ATCC No. 20892) and
12B (ATCC No. 20890) are examples of such strains. In addition,
there are 35 strains of the invention that produce more than 25% by
weight of total fatty acids as omega-6 fatty acids, more than any
previously known strain. While such strains may not be useful for
dietary purposes, they are useful as feedstock for chemical
synthesis of eicosanoids starting from omega-6 fatty acids.
In addition, the data reveal many strains of the invention which
produce a high proportion of total omega-3 fatty acids as C22:6w3.
In Table 4, 48 of the strains shown in Table 2 were compared to the
previously known strains, showing each of C20:5w3, C22:5w3 and
C22:6w3 as percent by weight of total omega-3 content. Fifteen
strains had at least 94% by weight of total omega-3 fatty acids as
C22:6w3, more than any previously known strain. Strain S8 (ATCC No.
20889) was an example of such strains. Eighteen strains had at
least 28% by weight of total omega-3 fatty acids as C20:5w3, more
than any previously known strain. Strain 12B (ATCC No. 20890) was
an example of such strains.
FIG. 2 illustrates the set of strains, isolated by the method in
Example 1, that have more than 67% omega-3 fatty acids (as % of
total fatty acids) and less than 10.6% omega-6 fatty acids (as % of
total fatty acids). All of the previously known strains had less
than 67% omega-3 fatty acids (as % of total fatty acids) and
greater than 10.6% omega-6 (as % of total fatty acids).
FIG. 3 illustrates the set of strains, isolated by the method in
Example 1, that have more than 67% omega-3 fatty acids (as % of
total fatty acids) and greater than 7.5% C20:5w3 (as % of total
fatty acids). All of the previously known strains had less than 67%
omega-3 fatty acids (as % of total fatty acids) and less than 7.8%
C20:5w3 (as % of total fatty acids).
TABLE 3
__________________________________________________________________________
PERCENT OF TOTAL FATTY ACIDS Total Total C16:0 C20:4w6 C20:5w3
C22:5w6 C22:5w3 C22:6w3 Other FA Omega 3 Omega 6 Strain
__________________________________________________________________________
LIST OF STRAINS AND COMPOSITIONS UNDER STANDARD SCREENING
CONDITIONS 30.4% 2.8% 6.6% 3.2% 0.2% 8.3% 48.5% 15.1% 6.0% 21 22.9%
0.4% 2.3% 15.5% 0.5% 47.0% 11.5% 49.7% 15.9% ATCC20889 14.9% 6.5%
12.0% 11.8% 0.4% 49.7% 4.7% 62.1% 18.3% U40-2 40.3% 1.7% 3.8% 8.6%
0.0% 8.2% 37.4% 12.0% 10.2% 21B 20.7% 0.4% 7.8% 0.0% 0.0% 1.1%
70.1% 8.9% 0.4% BG1 26.0% 5.7% 1.5% 9.7% 0.7% 9.7% 46.7% 11.9%
15.4% 56A 16.4% 1.4% 10.0% 1.9% 2.2% 46.4% 21.8% 58.6% 3.3% 11A-1
23.7% 3.3% 10.5% 1.9% 1.8% 29.9% 28.9% 42.2% 5.2% 4A-1 18.7% 6.9%
9.2% 11.9% 3.2% 25.2% 24.9% 37.5% 18.8% 17B 15.4% 4.2% 7.3% 9.5%
0.9% 51.2% 11.6% 59.3% 13.7% ATCC20891 22.3% 3.9% 7.6% 23.5% 0.5%
22.1% 20.2% 30.2% 27.4% S44 14.4% 2.3% 15.0% 18.4% 0.7% 43.8% 5.5%
59.4% 20.7% U30 22.1% 7.8% 3.1% 12.7% 1.0% 14.9% 38.3% 19.0% 20.5%
59A 18.1% 2.3% 6.9% 9.1% 0.8% 52.2% 10.6% 59.9% 11.4% U37-2 15.8%
3.9% 8.8% 11.6% 1.2% 53.3% 5.5% 63.3% 15.5% S50W 23.7% 3.8% 6.3%
6.9% 0.6% 43.0% 15.6% 50.0% 10.7% ATCC20891 10.0% 0.0% 0.0% 0.0%
0.0% 0.0% 90.0% 0.0% 0.0% UX 16.6% 6.3% 11.9% 13.3% 1.7% 43.0% 7.3%
56.6% 19.5% LW9 17.3% 2.3% 8.4% 11.4% 0.7% 53.6% 6.5% 62.6% 13.6%
C32-2 23.8% 1.2% 6.4% 2.5% 1.9% 34.4% 29.8% 42.6% 3.7% 5A-1 17.1%
5.2% 11.1% 7.6% 2.2% 27.2% 29.6% 40.4% 12.9% BG1 25.4% 2.2% 9.6%
7.0% 1.1% 46.0% 8.8% 56.7% 9.1% U3 16.9% 12.0% 6.6% 16.2% 0.4%
25.1% 22.8% 32.1% 28.2% 55B 26.3% 2.6% 8.6% 2.0% 2.5% 32.4% 25.5%
43.5% 4.6% 18A 19.4% 0.3% 9.8% 0.0% 0.3% 38.4% 31.7% 48.6% 0.3% 32B
16.0% 16.7% 8.6% 18.4% 0.0% 22.5% 17.7% 31.1% 35.1% 56B 18.6% 7.7%
11.4% 3.6% 4.3% 31.7% 22.7% 47.4% 11.2% SX2 17.8% 4.4% 16.2% 6.4%
3.7% 33.6% 17.8% 53.5% 10.9% 53B 16.8% 2.7% 13.8% 20.5% 1.4% 39.3%
5.5% 54.4% 23.3% S49 20.8% 8.0% 8.9% 6.4% 1.7% 33.9% 20.3% 44.5%
14.4% S3 14.8% 0.3% 3.7% 3.9% 0.0% 69.9% 7.4% 73.6% 4.2% 3A-1 28.1%
5.2% 12.7% 3.2% 0.9% 20.9% 29.0% 34.5% 8.4% 15A 20.9% 0.7% 8.5%
1.0% 0.0% 35.8% 33.0% 44.3% 1.7% 9A-1 15.7% 10.2% 8.8% 13.4% 1.5%
23.9% 26.3% 34.3% 23.7% 51B 16.2% 11.2% 7.8% 16.4% 1.5% 20.4% 26.5%
29.7% 27.6% 8A-1 20.5% 5.5% 8.6% 4.8% 2.7% 28.7% 29.2% 40.0% 10.3%
13A-1 16.1% 13.6% 11.1% 16.0% 0.0% 28.4% 14.8% 39.4% 29.6% 24B-2
16.9% 7.3% 16.4% 6.1% 0.0% 40.8% 12.4% 57.2% 13.4% 24B-1 16.2% 0.0%
10.9% 1.0% 0.0% 56.5% 15.5% 67.4% 1.0% 3B 17.0% 0.0% 5.0% 2.3% 0.0%
73.4% 2.3% 78.3% 2.3% SBG5 20.8% 4.5% 5.8% 3.8% 1.0% 22.7% 41.3%
29.5% 8.4% 16B 19.0% 14.0% 8.3% 18.9% 0.7% 23.9% 15.2% 32.9% 32.9%
6A-1 18.0% 0.3% 10.1% 0.0% 0.0% 48.9% 22.7% 59.0% 0.3% 33B
16.7% 5.5% 14.8% 8.5% 1.7% 31.8% 21.0% 48.3% 13.9% B40 15.0% 1.0%
11.7% 2.1% 0.9% 62.3% 6.9% 74.9% 3.1% 28A 17.8% 18.5% 8.1% 20.5%
0.0% 22.1% 12.9% 30.2% 39.0% 43B 16.9% 0.0% 3.4% 2.7% 0.0% 61.2%
15.8% 64.6% 2.7% 1A-1 15.6% 2.7% 11.4% 10.9% 0.8% 53.7% 4.9% 65.9%
13.6% U41-2 16.5% 0.7% 3.9% 3.9% 0.0% 68.4% 6.7% 72.2% 4.6% 56B
14.4% 0.9% 10.9% 2.5% 1.0% 66.4% 3.8% 78.3% 3.4% 46A 17.6% 0.0%
2.4% 3.3% 0.0% 66.3% 10.4% 68.7% 3.3% 15A-1 25.0% 0.0% 3.3% 0.0%
1.4% 53.2% 17.1% 57.9% 0.0% 13A 16.1% 13.4% 9.3% 13.6% 0.0% 32.3%
15.3% 41.6% 27.0% 37B 16.5% 9.1% 13.2% 6.7% 0.0% 38.9% 15.6% 52.1%
15.9% 43B 16.1% 12.4% 12.0% 15.7% 0.8% 30.5% 12.5% 43.3% 28.1% 17B
13.8% 0.8% 11.5% 2.8% 0.0% 67.0% 4.1% 78.6% 3.6% 27A 17.5% 18.6%
9.0% 19.5% 0.0% 21.7% 13.7% 30.7% 38.1% 46B 21.4% 1.4% 18.9% 0.0%
5.0% 43.5% 9.9% 67.3% 1.4% ATCC20890 17.7% 0.0% 0.6% 4.4% 0.0%
68.2% 9.1% 68.8% 4.4% 5A 17.6% 16.0% 9.6% 18.8% 0.0% 25.6% 12.4%
35.2% 34.8% 28B-2 14.0% 0.9% 13.2% 1.6% 0.0% 64.7% 5.5% 77.9% 2.6%
27B 19.5% 2.9% 16.6% 1.1% 1.6% 30.2% 28.1% 48.5% 4.0% 49B 17.2%
0.7% 6.8% 2.7% 0.0% 63.0% 9.6% 69.8% 3.4% 18B 14.4% 3.5% 13.5%
26.0% 1.0% 37.2% 4.4% 51.6% 29.5% S49-2 16.1% 2.2% 15.7% 21.6% 0.0%
36.7% 7.8% 52.4% 23.7% 20B 17.3% 4.7% 14.3% 7.2% 2.9% 30.2% 23.5%
47.3% 11.9% 8B 11.5% 3.3% 11.3% 6.5% 1.1% 59.9% 6.5% 72.2% 9.8% 13B
16.6% 0.7% 10.7% 1.6% 0.0% 59.7% 10.8% 70.4% 2.2% 26A 16.1% 3.3%
13.5% 23.8% 0.0% 38.7% 4.7% 52.2% 27.1% S42 15.6% 0.6% 12.1% 0.0%
0.0% 60.2% 11.5% 72.3% 0.6% 35B 19.5% 0.0% 1.4% 3.4% 0.0% 66.6%
9.1% 68.0% 3.4% 42A 18.9% 3.5% 12.7% 25.0% 0.0% 35.0% 5.0% 47.6%
28.5% 40A 25.2% 3.3% 9.3% 21.8% 0.0% 30.3% 10.1% 39.6% 25.1% S50C
17.6% 11.1% 13.2% 14.1% 1.3% 28.7% 14.0% 43.2% 25.2% 59A 19.9% 0.0%
5.5% 1.9% 0.0% 66.8% 6.0% 72.3% 1.9% SBG9 15.4% 3.1% 13.2% 26.1%
0.0% 35.8% 6.5% 49.1% 29.1% 21B 18.9% 0.7% 11.6% 0.0% 0.0% 59.1%
9.7% 70.7% 0.7% 2B 14.1% 1.1% 12.4% 2.0% 0.0% 65.2% 5.2% 77.6% 3.1%
1B 22.2% 16.2% 6.3% 17.7% 0.0% 18.1% 19.5% 24.4% 33.8% 55B 16.0%
1.0% 4.5% 0.0% 0.0% 69.5% 9.0% 74.0% 1.0% 3A 17.0% 4.3% 12.4% 29.8%
0.0% 34.0% 2.5% 46.4% 34.1% 9B 15.4% 4.3% 8.7% 13.2% 0.0% 53.2%
5.1% 62.0% 17.5% U24 14.2% 3.1% 12.0% 20.0% 1.1% 35.2% 14.3% 48.3%
23.2% U28 16.8% 14.6% 10.1% 16.0% 0.6% 27.7% 14.0% 38.5% 30.7%
28B-1 23.2% 1.9% 8.3% 1.1% 2.3% 22.7% 40.4% 33.3% 3.0% 44B 24.6%
15.8% 8.7% 16.0% 0.0% 15.3% 19.6% 24.0% 31.8% 54B 15.5% 0.0% 1.3%
2.9% 0.0% 72.7% 7.6% 74.0% 2.9% 55A
18.4% 1.0% 5.0% 3.0% 0.0% 66.2% 6.4% 71.3% 3.9% 49A 18.6% 15.3%
9.4% 18.0% 0.0% 27.3% 11.4% 36.7% 33.3% 51A 23.5% 13.1% 7.3% 17.9%
0.0% 26.7% 11.4% 34.0% 31.0% 14A-1 13.3% 1.1% 14.5% 0.9% 0.0% 64.6%
5.6% 79.1% 2.0% 25B 22.9% 2.4% 10.3% 21.5% 0.0% 26.5% 16.4% 36.9%
23.9% 41A 16.8% 1.0% 9.7% 2.7% 0.0% 58.3% 11.5% 68.0% 3.7% 24A 0.4%
8.5% 14.1% 10.2% 2.1% 27.6% 37.0% 43.8% 18.8% 61A 30.5% 0.0% 7.1%
0.0% 0.0% 0.6% 61.8% 7.7% 0.0% BRBG 18.2% 14.9% 8.3% 18.7% 0.0%
24.4% 15.5% 32.7% 33.6% 17A 17.4% 2.0% 9.3% 2.8% 0.0% 55.7% 12.7%
65.0% 4.9% 60A 14.1% 0.8% 13.0% 1.2% 0.0% 67.8% 3.1% 80.8% 2.0% 26B
17.8% 5.0% 6.9% 15.0% 1.5% 47.4% 6.4% 55.8% 20.0% ATCC20888 16.0%
0.0% 1.8% 2.0% 0.0% 70.8% 9.4% 72.6% 2.0% 2A 24.6% 0.0% 4.0% 0.0%
0.0% 49.4% 22.0% 53.4% 0.0% 44A 17.4% 1.8% 0.0% 2.9% 0.0% 55.3%
23.3% 55.3% 4.6% 14A 23.3% 1.3% 4.6% 0.0% 0.0% 12.6% 58.1% 17.3%
1.3% 41B 19.3% 0.0% 1.1% 3.8% 0.0% 66.6% 9.1% 67.8% 3.8% 66A 18.6%
15.6% 8.3% 17.1% 1.1% 24.6% 14.8% 33.9% 32.7% 11A 19.6% 5.1% 10.1%
27.2% 0.0% 27.5% 10.6% 37.5% 32.3% 2X 15.7% 2.4% 14.0% 25.7% 0.0%
36.7% 5.4% 50.8% 28.1% 33A 14.6% 1.5% 13.5% 0.0% 0.0% 66.0% 4.3%
79.5% 1.5% ATCC20892 PRIOR STRAINS 15.7% 3.9% 3.7% 8.1% 0.0% 55.1%
13.5% 58.8% 12.0% ATCC34304 28.2% 1.6% 6.9% 11.4% 0.0% 17.8% 34.1%
24.7% 12.9% ATCC24473 15.2% 2.9% 7.7% 9.8% 0.6% 54.6% 9.2% 62.9%
12.7% ATCC28211 23.2% 10.7% 4.3% 12.6% 1.5% 20.6% 27.0% 26.4% 23.4%
ATCC28209 13.2% 6.3% 6.9% 4.3% 0.0% 60.1% 9.1% 67.0% 10.6%
ATCC28210
__________________________________________________________________________
TABLE 4 ______________________________________ EPA DPA DHA C20:5w3
C22:5w3 C22:6w3 Strain ______________________________________
COMPOSITION OF OMEGA 3 FATTY ACID FRACTION 44.0% 1.1% 54.9% 21 4.6%
0.9% 94.5% ATCC20889 19.3% 0.7% 80.0% U40-2 31.9% 0.0% 68.1% 21B
87.9% 0.0% 12.1% BRBG1 12.5% 6.1% 81.5% 56A 17.0% 3.7% 79.3% 11A-1
24.9% 4.3% 70.8% 4A-1 24.4% 8.4% 67.2% 17B 12.2% 1.5% 86.3%
ATCC20891 25.1% 1.7% 73.2% S44 25.2% 1.1% 73.7% U30 16.2% 5.4%
78.4% 59A 11.5% 1.4% 87.1% U37-2 14.0% 1.9% 84.2% S50W 12.7% 1.3%
86.0% ATCC20891 -- -- -- UX 21.0% 2.9% 76.1% LWN9 13.4% 1.0% 85.6%
C32-2 15.0% 4.3% 80.7% 5A-1 27.4% 5.4% 67.2% BRBG1 17.0% 1.9% 81.1%
U3 20.5% 1.3% 78.2% 55B 19.8% 5.8% 74.4% 18A 20.1% 0.7% 79.2% 32B
27.8% 0.0% 72.2% 56B 24.1% 9.1% 66.9% SX2 30.3% 6.9% 62.8% 53B
25.3% 2.5% 72.2% S49 19.9% 3.8% 76.3% S3 5.0% 0.0% 95.0% 3A-1 36.9%
2.6% 60.5% 15A 19.3% 0.0% 80.7% 9A-1 25.8% 4.4% 69.8% 51B 26.3%
5.0% 68.7% 8A-1 21.6% 6.7% 71.7% 13A-1 28.0% 0.0% 72.0% 24B-2 28.7%
0.0% 71.3% 24B-1 16.2% 0.0% 83.8% 3B 6.3% 0.0% 93.7% SBG5 19.7%
3.3% 77.0% 16B 25.2% 2.1% 72.6% 6A-1 17.1% 0.0% 82.9% 33B 30.5%
3.6% 65.9% B40 15.6% 1.2% 83.1% 28A 26.8% 0.0% 73.2% 43B 5.2% 0.0%
94.8% 1A-1 17.4% 1.2% 81.5% U41-2 5.4% 0.0% 94.6% 56B 13.9% 1.3%
84.8% 46A 3.5% 0.0% 96.5% 15A-1 5.8% 2.4% 91.8% 13A 22.3% 0.0%
77.7% 37B 25.4% 0.0% 74.6% 43B 27.7% 1.9% 70.3% 17B 14.7% 0.0%
85.3% 27A 29.2% 0.0% 70.8% 46B 28.0% 7.5% 64.5% ATCC20890 0.9% 0.0%
99.1% 5A 27.3% 0.0% 72.7% 28B-2 16.9% 0.0% 83.1% 27B 34.3% 3.4%
62.3% 49B 9.7% 0.0% 90.3% 18B 26.1% 1.9% 71.9% S49-2 29.9% 0.0%
70.1% 20B 30.1% 6.2% 63.7% 8B 15.6% 1.5% 82.9% 13B 15.2% 0.0% 84.8%
26A 25.9% 0.0% 74.1% S42 16.7% 0.0% 83.3% 35B 2.1% 0.0% 97.9% 42A
26.6% 0.0% 73.4% 40A 23.4% 0.0% 76.6% S50C 30.6% 2.9% 66.4% 59A
7.6% 0.0% 92.4% SBG9 27.0% 0.0% 73.0% 21B 16.4% 0.0% 83.6% 2B 15.9%
0.0% 84.1% 1B 25.9% 0.0% 74.1% 55B 6.0% 0.0% 94.0% 3A 26.7% 0.0%
73.3% 9B 14.1% 0.0% 85.9% U24 24.9% 2.2% 72.9% U28 26.4% 1.5% 72.1%
28B-1 24.8% 6.9% 68.3% 44B 36.4% 0.0% 63.6% 54B 1.8% 0.0% 98.2% 55A
7.1% 0.0% 92.9% 49A 25.6% 0.0% 74.4% 51A 21.5% 0.0% 78.5% 14A-1
18.4% 0.0% 81.6% 25B 28.1% 0.0% 71.9% 41A 14.3% 0.0% 85.7% 24A
32.3% 4.8% 63.0% 61A 91.6% 0.0% 8.4% BRBG 25.5% 0.0% 74.5% 17A
14.4% 0.0% 85.6% 60A 16.1% 0.0% 83.9% 26B 12.4% 2.7% 84.9%
ATCC20888 2.5% 0.0% 97.5% 2A 7.5% 0.0% 92.5% 44A 0.0% 0.0% 100.0%
14A 26.7% 0.0% 73.3% 41B 1.7% 0.0% 98.3% 66A 24.5% 3.1% 72.4% 11A
26.8% 0.0% 73.2% 2X 27.6% 0.0% 72.4% 33A 17.0% 0.0% 83.0% ATCC20892
PRIOR STRAINS 6.4% 0.0% 93.6% ATCC34304 27.9% 0.0% 72.1% ATCC24473
12.2% 1.0% 86.8% ATCC28211 16.4% 5.6% 78.1% ATCC28209 10.3% 0.0%
89.7% ATCC28210 ______________________________________
Example 6. Enhanced growth rates of strains isolated by method in
Example 1 compared to ATCC strains (previously known strains
Cells of Schizochytrium sp. S31 (ATCC No. 20888), Schizochytrium
sp. S8 (ATCC No. 20889), Thraustochytrium sp. S42, Thraustochytrium
sp. U42-2, Thraustochytrium sp. S42 and U30, (all isolated by the
method of Example 1) and Thraustochytrium aureum (ATCC #28211) and
Schizochytrium aggregatum (ATCC #28209) (previously known strains)
were picked from solid F-1 medium and placed into 50 ml of M-5
medium. This medium consists of (on a per liter basis): Yeast
Extract, 1 g; NaCl, 25 g; MgSO.sub.4.7H.sub.2 O, 5 g; KCl, 1 g;
CaCl.sub.2, 200 mg; glucose, 5 g; glutamate, 5 g; KH.sub.2
PO.sub.4, 1 g; PII metals, 5 ml; A-vitamins solution, 1 ml; and
antibiotic solution, 1 ml. The pH of the solution was adjusted to
7.0 and the solution was filter sterilized. After three days of
growth on an orbital shaker (200 rpm, 27.degree. C.), 1-2 ml of
each culture was transferred to another flask of M-5 medium and
placed on the shaker for 2 days. The cultures (1-2 ml) were then
transferred to another flask of M-5 medium and placed on the shaker
for 1 day. This process ensured that all cultures were in the
exponential phase of growth. These later cultures were then used to
inoculate two 250 ml flasks of M-5 medium for each strain. These
flasks were than placed on shakers at 25.degree. C. and 30.degree.
C., and changes in their optical density were monitored on a
Beckman DB-G spectrophotometer (660nm, 1 cm path length). Optical
density readings were taken at the following times: 0, 6, 10, 14,
17.25, 20.25 and 22.75 hours. Exponential growth rates
(doublings/day) were then calculated from the optical density data
by the method of Sorokin (1973). The results are presented in Table
5 and illustrated (normalized to the growth of strain U30 at
25.degree. C.) in FIG. 5. The data indicate that the strains
isolated by the method in Example 1 have much higher growth rates
than the previously known ATCC strains at both 25.degree. C. and
30.degree. C., even under the optimized phosphate levels essential
for continuous growth. Strains of Thraustochytriales isolated from
cold Antarctic waters have not been shown to grow at 30.degree.
C.
TABLE 5 ______________________________________ Exponential Growth
Rate (doublings/day) Strain 25.degree. C. 30.degree. C.
______________________________________ S31* 8.5 9.4 U40-2* 5.8 6.0
S8* 7.1 8.8 S42* 6.6 8.3 U30* 5.5 7.3 28209** 4.6 5.0 28210** 3.5
4.5 28211** 4.2 5.7 34304** 2.7 3.7 24473** 4.6 5.3
______________________________________ *strain isolated by method
in Example 1 **previously known ATCC strain
Example 7. Enhanced production characteristics (growth and lipid
induction) of strains isolated by method in Example 1 compared to
ATCC strains (prior art strains)
Cells of Schizochytrium sp. S31 (ATCC No. 20888), Schizochytrium
sp. S8 (ATCC No. 20889) (both isolated by the method of Example 1)
and Thraustochytrium aureum (ATCC #28211) and Schizochytrium
aggregatum (ATCC #28209) (prior art strains) were picked from solid
F-1 medium and placed into 50 ml of M-5 medium (see Example 5) The
pH of the solution was adjusted to 7.0 and the solution was filter
sterilized. After three days of growth on an orbital shaker (200
rpm, 27.degree. C.), 1-2 ml of each culture was transferred to
another flask of M-5 medium and placed on the shaker for 2 days.
The ash-free dry weights for each of these cultures were then
quickly determined and 3.29 mg of each culture was pipetted into
two 250 ml erlenmeyer flasks containing 50 ml of M-5 medium. These
flasks were placed on a rotary shaker (200 rpm, 27.degree. C.).
After 24 hours 20 ml portions of each culture were then
centrifuged, the supernatants discarded, and the cells transferred
to 250 ml erlenmeyer flasks containing 50 ml of M-5 medium without
any glutamate (N-source). The flasks were placed back on the
shaker, and after another 12 hours they were sampled to determine
ash-free dry weights and quantify fatty acid contents by the method
of Lepage and Roy (1984). The results are illustrated (normalized
to the yields of ATCC No. 28211, previously known strain) in FIG.
6. The results indicate that the strains isolated by the method of
Example 1 produced 2-3 times as much ash-free dry weight in the
same period of time, under a combination of exponential growth and
nitrogen limitation (for lipid induction) as the prior art ATCC
strains. In addition, higher yields of total fatty acids and
omega-3 fatty acids were obtained from strains of the present
invention with strains S31 (ATCC No. 20888) producing 3-4 times as
much omega-3 fatty acids as the prior art ATCC strains.
Example 8. Enhanced salinity tolerance and fatty acid production by
strains isolated by method in Example 1
Strains of 4 species of Thraustochytrids, Schizochytrium sp. S31
(ATCC No. 20888) and Thraustochytrium sp. U42-2 (ATCC No. 20891)
(both isolated and screened by the method of Example 1), and S.
aggregatum (ATCC 28209) and T. aureum (ATCC 28210) (obtained from
the American Type Culture Collection) were picked from solid F-1
medium and incubated for 3-4 days at 27.degree. C. on a rotary
shaker (200 rpm). A range of differing salinity medium was prepared
by making the following dilutions of M medium salts (NaCl, 25 g/1;
MgSO.sub.4.7H.sub.2 O, 5 g/1; KCl, 1 g/1; CaCl.sub.2, 200 mg/1: 1)
100% (w/v M medium salts; 2) 80% (v/v) M medium, 20% (v/v)
distilled water; 3) 60% (v/v) M medium, 40% (v/v) distilled water;
4) 40% (v/v) M medium, 60% (v/v) distilled water; 5) 20% (v/v) M
medium, 80% distilled water; 6) 15% (v/v) M medium, 85% (v/v)
distilled water; 7) 10% (v/v) M medium, 90% (v/v) distilled water;
8) 7% (v/v) M medium, 93% (v/v) distilled water; 9) 3% (v/v) M
medium, 97% (v/v) distilled water; 10) 1.5% (v/v) M medium, 98.5%
(v/v) distilled water. The following nutrients were added to the
treatments (per liter): glucose, 5 g; glutamate, 5 g; yeast ext., 1
g; (NH4)2S04, 200 mg; NaHC03, 200 mg; KH.sub.2 PO.sub.4,1 g/l; PII
metals, 5 ml; A-vitamins solution,1 ml; and antibiotics solution, 2
ml. Fifty ml of each of these treatments were inoculated with1 ml
of the cells growing in the F-1 medium. These cultures were placed
on an orbital shaker (200 rpm) and maintained at 27.degree. C. for
48 hr. The cells were harvested by centrifugation and total fatty
acids determined by gas chromatography. The results are illustrated
in FIG. 7. Thraustochytrium sp. U42-2 (ATCC No. 20891) isolated by
the method of Example 1 can yield almost twice the amount of fatty
acids produced by T. aureum (ATCC 28210) and over 8 times the
amount of fatty acids produced by S. aggregatum (ATCC 28209).
Additionally, U42-2 appears to have a wider salinity tolerance at
the upper end of the salinity range evaluated. Schizochytrium sp.
S31 (ATCC No. 20888), also isolated by the method in Example 1,
exhibited both a high fatty acid yield (2.5 to 10 times that of the
previously known ATCC strains) and a much wider range of salinity
tolerance than the ATCC strains. Additionally, Schizochytrium sp.
S31 (ATCC No. 20888) grows best at very low salinities. This
property provides a strong economic advantage when considering
commercial production, both because of the corrosive effects of
saline waters on metal reactors, and because of problems associated
with the disposal of saline waters.
Example 9. Cultivation/Low Salinity
Fifty ml of M/10-5 culture media in a 250 ml erlenmeyer flask was
inoculated with a colony of Schizochytrium sp. S31 (ATCC No. 20888)
picked from an agar slant. The M/10-5 media contains: 1000 ml
deionized water, 2.5 g NaCl, 0.5 g MgSO.sub.4 7H.sub.2 O, 0.1 g
KCl, 0.02 g CaCl.sub.2, 1.0 g KH.sub.2 PO.sub.4, 1.0 g yeast
extract, 5.0 g glucose, 5.0 g glutamic acids, 0.2 g NaHC03, 5 ml
PII trace metals, 2 ml vitamin mix, and 2 ml antibiotic mix. The
culture was incubated at 30.degree. C. on a rotary shaker (200
rpm). After 2 days the culture was at a moderate density and
actively growing. 20 ml of this actively growing culture was used
to inoculate a 2 liter fermenter containing 1700 ml of the same
culture media except the concentration of the glucose and glutamate
had been increased to 40 g/1 (M/10-40 media). The fermenter was
maintained at 30.degree. C., with aeration at 1 vol/vol/min, and
mixing at 300 rpm. After 48 hr, the concentration of cells in the
fermenter was 21.7 g/l. The cells were harvested by centrifugation,
lyophilized, and stored under N.sub.2.
The total fatty acid content and omega-3 fatty acid content was
determined by gas chromatography. The total fatty acid content of
the final product was 39.0% ash-free dry weight. The omega-3 highly
unsaturated fatty acid content (C20:5w3, C22:5w3 and C22:6w3) of
the microbial product was 25.6% of the ash-free dry weight. The ash
content of the sample was 7.0%.
Example 10
Growth and gas chromatographic analysis of fatty acid production by
various strains as described in example 5 revealed differences in
fatty acid diversity. Strains of the present invention synthesized
fewer different fatty acids than previously available strains.
Lower diversity of fatty acids is advantageous in fatty acid
purification since there are fewer impurities to be separated. For
food supplement purposes, fewer different fatty acids is
advantageous because the likelihood of ingesting unwanted fatty
acids is reduced. Table 6 shows the number of different highly
unsaturated fatty acids present, at concentrations greater than 1%
by weight of total fatty acids for previously known strains,
designated by ATCC number and various strains of the present
invention.
TABLE 6 ______________________________________ No. of Different
Fatty Acids at 1% or Greater Strain % of Total Fatty Acids
______________________________________ 34304** 8 28211** 8 24473**
10 28209** 13 28210** 8 S31* 5 S8* 6 79B* 6
______________________________________ *strain isolated by the
method in Example 1 **previously known ATCC strain
Example 11. Recovery
Fifty ml of M5 culture media in a 250 ml erlenmeyer flask was
inoculated with a colony of Schizochytrium sp. S31 (ATCC No. 20888)
picked from an agar slant. The M5 media contains: 1000 ml deionized
water, 25.0 g NaCl, 5.0 g MgSO4.7H.sub.2 O, 1.0 g KCl, 0.2 g
CaCl.sub.2, 1.0 g KH.sub.2 PO.sub.4, 1.0 g yeast extract, 5.0 g
glucose, 5.0 g glutamic acid, 0.2 g NaHCO.sub.3,5 ml PII trace
metals, 2 ml vitamin mix, and 2 ml antibiotic mix. The culture was
incubated at 30.degree. C. on a rotary shaker (200 rpm). After 2
days the culture was at a moderate density and actively growing. 20
ml of this actively growing culture was used to inoculate an 1
liter fermenter containing 1000 ml of the same culture media except
the concentration of the glucose and glutamate had been increased
to 40 g/l (M20 media). The fermenter was maintain at 30.degree. C.
and pH 7.4, with aeration at 1 vol/min, and mixing at 400 rpm.
After 48 hr, the concentration of the cells in the fermenter was
18.5 g/l. Aeration and mixing in the fermenter was turned off.
Within 2-4 minutes, the cells flocculated and settled in the bottom
250 ml of the fermenter. This concentrated zone of cells had a cell
concentration of 72 g/l. This zone of cells can be siphoned from
the fermenter, and: (1) transferred to another reactor for a period
of nitrogen limitation (e.g., combining the highly concentrated
production of several fermenters); or (2) harvested directly by
centrifugation or filtration. By preconcentrating the cells in this
manner, 60-80% less water has to be processed to recover the
cells.
Example 12. Utilization of a variety of carbon and nitrogen
sources
Fifty ml of M5 culture media in a 250 ml erlenmeyer flask was
inoculated with a colony of Schizochytrium sp. S31 (ATCC No. 20888)
or Thraustochytrium sp. U42-2 (ATCC No. 20891) picked from an agar
slant. The M5 media was described in Example 4 except for 2 ml
vitamin mix, and 2 ml antibiotic mix. The culture was incubated at
30.degree. C. on a rotary shaker (200 rpm). After 2 days the
culture was at a moderate density and actively growing. This
culture was used to inoculate flasks of M5 media with one of the
following substituted for the glucose (at 5 g/l): dextrin,
sorbitol, fructose, lactose, maltose, sucrose, corn starch, wheat
starch, potato starch, ground corn; or one of the following
substituted for the glutamate (at 5 g/l): gelysate, peptone,
tryptone, casein, corn steep liquor, urea, nitrate, ammonium, whey,
or corn gluten meal. The cultures were incubated for 48 hours on a
rotary shaker (200 rpm, 27.degree. C.). The relative culture
densities, representing growth on the different organic substrates,
are illustrated in Tables 7-8.
TABLE 7 ______________________________________ Utilization of
Nitrogen Sources Strains Thraustochytrium Schizochytrium sp. U42-2
sp. S31 N-Source ATCC No. 20891 ATCC No. 20888
______________________________________ glutamate +++ +++ gelysate
+++ +++ peptone ++ ++ tryptone ++ ++ casein ++ ++ corn steep +++
+++ liquor urea + ++ nitrate ++ +++ ammonium + +++ whey +++ +++
corn gluten +++ +++ meal ______________________________________ +++
= high growth ++ = medium growth + = low growth 0 = no growth
TABLE 8 ______________________________________ Utilization of
Organic Carbon Sources. Strains Thraustochytrium Schizochytrium sp.
U42-2 sp. S31 C-Source ATCC No. 20891 ATCC No. 20888
______________________________________ glucose +++ +++ dextrin +++
+++ sorbitol + + fructose + +++ lactose + + maltose +++ + sucrose +
+ corn starch +++ + wheat starch +++ + potato starch +++ + ground
corn +++ 0 ______________________________________ +++ = high growth
++ = medium growth + = low growth 0 = no growth
Example 13. Feeding of thraustochytrid-based feed supplement to
brine shrimp to increase their omega-3 HUFA content
Cellular biomass of Thraustochytrium sp. 12B (ATCC 20890) was
produced in shake flasks in M-5 medium (see Example 6) at
25.degree. C. Cellular biomass of Thraustochytrium sp. S31 (ATCC
20888) was produced in shake flasks in M-5/10 medium (see Example
9) at 27.degree. C. The cells of each strain were harvested by
centrifugation. The pellet was washed once with distilled water and
recentrifuged to produce a 50% solids paste. The resulting paste
was resuspended in sea water and then added to an adult brine
shrimp culture as a feed supplement. The brine shrimp had
previously been reared on agricultural waste products and as a
result their omega-3 HUFA content was very low, only 1.3-2.3% of
total fatty acids (wild-caught brine shrimp have an average omega-3
HUFA content of 6-8% total fatty acids). The brine shrimp (2-3/mL)
were held in a 1 liter beaker filled with sea water and an airstone
was utilized to aerate and mix the culture. After addition of the
feed supplement, samples of the brine shrimp were periodically
harvested, washed, and their fatty acid content determined by gas
chromatography. The results are illustrated in FIGS. 8 -9. When fed
the thraustochytrid-based feed supplement as a finishing feed, the
omega-3 content of the brine shrimp can be raised to that of
wild-type brine shrimp within 5 hours if fed strain 12B or within
11 hours when fed strain S31. The omega-3 HUFA content of the brine
shrimp can be greatly enhanced over that of the wild type if fed
these feed supplements for up to 24 hours. Additionally, these feed
supplements greatly increase the DHA content of the brine shrimp,
which is generally only reported in trace levels in wild-caught
brine shrimp.
Example 14. Feeding of thraustochytrid-based feed supplement to
laying hens to produce omega-3 HUFA enriched eggs
Cellular biomass of Thraustochytrium sp. S31 (ATCC 20888) was
produced in a 10 liter fermenter in M-5/10 medium (see Example 9)
at 27.degree. C. The cells of Thraustochytrium sp. S31 (ATCC 20888)
were harvested by centrifugation, washed once with distilled water
and recentrifuged to produce a 50% solids paste. This cell paste
was then treated in one of two ways: lyophilized; or 2) mixed with
ground corn to produce a 70% solids paste and then extruded at
90.degree.-120.degree. C. and air dried. The resulting dried
products were then ground, analyzed for omega-3 HUFA content, and
mixed into layers rations at a level to provide 400 mg of omega-3
HUFA per day to the laying hens (400 mg omega-3 HUFA/100 grams
layers ration). The resulting eggs were sampled over a period of
approximately 45 days and analyzed by gas chromatography for
omega-3 HUFA's. Eggs with up to 200 -425 mg omega-3 HUFA's/egg were
produced by the hen fed omega-3 supplement. When cooked, these eggs
did not exhibit any fishy odors. The control hens produced eggs
with only approximately 20 mg omega-3 HUFA/egg. There was no
significant difference between the number of eggs laid by the
control group and the hen fed the omega-3 supplement. There was
also no difference in the color of yolks of the eggs produced with
the feed supplement and the control diet.
Example 15. Production of high purity (>90% purity omega-3 HUFA
or >90% purity HUFA fatty acids mixtures)
Cellular biomass of Thraustochytrium sp. S31 (ATCC 20888) was
produced in a 10 liter fermenter in M-5/10 medium (see Example 9)
at 27.degree. C. The cells of this strain were harvested by
centrifugation. Approximately 5 g of the cell paste was placed in
the 350 mL stainless steel grinding chamber of a Bead-Beater bead
mill which was filled 1/2 way with 0.5 mm glass beads. The
remaining volumes of the chamber was filled with reagent grade MeOH
and the cells homogenized for two 3 minute periods. During the bead
mill operation, the stainless steel chamber was kept cold by an
attached ice bath. The solution of broken cells was poured into a
flask to which was added both chloroform and a 2 M NaCl solution in
water to bring the final solution to approximately 1:1:0.9
(chloroform:MeOH:water). The solution was then poured into a
separatory funnel and shaken several times to help move the lipids
into the chloroform fraction. After the solution was allowed to
settle for several minutes, the chloroform fraction was collected
into a flask, another portion of fresh chloroform added to the
separatory funnel and the extraction repeated. This fraction of
chloroform was then collected from the separatory funnel and the
two chloroform portions combined. The chloroform was then removed
(and recovered) by using a roto-vap rotary vacuum evaporation
device operated at 40.degree. C. A portion (300 mg) of the
remaining lipids was removed and hydrolyzed for 6 hours at
60.degree. C. (under nitrogen gas) in 50 mL of solution of
methanolic NaOH (10 mL of 0.3 N NaOH diluted to 100 mL with MeOH)
in a 150 mL teflon lined screw capped bottle. The nonsaponifiable
materials (sterols, hydrocarbons, etc.) were then removed by phase
separating the solution with two 50 mL portions of petroleum either
in a separatory funnel, discarding the ether fraction each time.
The remaining solution was then acidified by addition of 3 mL of 6
N HCl and the free fatty acids extracted with two 50 mL portions of
petroleum ether. Five mL portion of the ether solution containing
the free fatty acids was placed in three 13 mm.times.100 mm test
tubes and the ether removed by blowing down the solution under a
flow of nitrogen gas. Two mL portions of either petroleum ether,
hexane or acetone were then added to one of tubes, which was then
caped and placed in a solution of dry ice and ethanol (-72.degree.
to -74.degree. C.) to allow the non-HUFA fatty acids to
crystallize. When crystallization appeared complete, the culture
tubes were placed in 50 mL polycarbonate centrifuge tubes that had
been filled with finely powdered dry ice. These tubes were then
placed in a refrigerated centrifuge at -10.degree. C. and
centrifuged for 3-5 minutes to 10,000 rpm. The supernatant was then
quickly removed from each tube with a pasteur pipet and placed in a
clean culture tube. The solvent was removed from the supernatants
by blowing down under N.sub.2. The fatty acids were then methylated
in methanolic H.sub.2 SO.sub.4 (4 mL H.sub.2 SO.sub.4 in 96 mL
MeoH) at 100.degree. C. for 1 hr. in teflon lined, screw capped
tubes under N.sub.2. The fatty acid methyl esters were then
quantified by gas chromatography (HP 5890 gas chromatograph,
Supelco SP 2330 column; column tepm=200.degree. C.; detector and
injector temp=250.degree. C.; carrier gas=nitrogen). The
composition of the fatty acid mixtures obtained were: (ether) 93.1%
HUFA's-23.4% C22:5n- 6+69.7% 22.6n-3:(hexane) 91.5% HUFA's-66.8%
22.6n-3+22.1% 22:5n-6.degree.2.6% 20:5n-3; (acetone) 90.0%
HUFA's-65.6% 22:6n-3+21.8n-6+2.6% 20:5n-3.
A fatty acid mixture containing >90% omega-3 UFA's can be
obtained by running the above process on harvested biomass of the
strain of thraustochytrid such as 12B (ATCC 20890).
General Concluding Remarks
The following novel strains, isolated according to the method of
the invention, were placed on deposit at the American Type Culture
Collection (ATCC), Rockville, Md, as exemplars of the organisms
disclosed and claimed herein.
______________________________________ Strain ATCC No. Deposit Date
______________________________________ Schizochytrium S31 20888
8/8/88 Schizochytrium S8 20889 8/8/88 Schizochytrium 12B 20890
8/8/88 Thraustochytrium U42-2 20891 8/8/88 Schizochytrium 23B 20892
8/8/88 ______________________________________
The present invention, while disclosed in terms of specific
organism strains, is intended to include all such methods and
strains obtainable and useful according to the teachings disclosed
herein, including all such substitutions, modifications, and
optimizations as would be available expedients to those of ordinary
skill in the art.
REFERENCES
Ainsworth, G. C. (1973) "Introduction and keys to the higher taxa."
In: The Fungi. An Advanced Treatise. Vol. 4B, G. C. Ainsworth et
al. (eds.), Academic Press, New York, pp. 107.
Bahnweg, G. & Jackle, I (1986) "A new approach to taxonomy of
the Thraustochytriales and Lybrinthulales." In: The Biology of
Marine Fungi, S. T. Moss (ed.), Cambridge University Press, London,
pp. 131-140.
Barr, J. S. (1981) "The phylogenetic and taxonomic implications of
flagellar rootlet morphology among zoosporic fungi." BioSystems
14:359-370.
Barr, J. S. (1983) "The zoosporic grouping of plant pathogens." In:
Zoosporic Plant Pathogens: a modern perspective, S. T. Buczacki
(ed.), Academic Press, pp. 43-83.
Bartnicki-Garcia, S. (1988) "The cell wall: a crucial structure in
fungal evolution." In: Evolutionary Biology of the Fungi, A. D. M.
Rayner et al. (eds.), Cambridge University Press, pp. 389-403.
CalBiochem Co. (1987). Biochemical/Immunochemical Catalog. Behring
Diagnostics, La Jolla, Calif.
Cavalier-Smith, T. (1975) "The origin of nuclei and of eukaryotic
cells." Nature 256:463-468.
Cavalier-Smith, T. (1983) "A 6-kingdom classification and a unified
phylogeny." In: Endocytobiology II: Intracellular Space as
Oligogenetic System, H. E. A. Schenk and W. Schwemmler (eds.), De
Gruyter (Berlin), pp. 1027-1034.
Chamberlain, A. H. and Moss, S. T. (1988) "The thraustochytrids: a
protist group with mixed affinities." BioSystems 21:341-349.
Cerda-Olmeda, E. & Lipson, E. (1987) Phycomyes, Cold Springs
Harbor Laboratory, Cold Springs Harbor, N.Y.
Dick, M. W. (1973) "Saprolegniales." In: The Fungi. An Advanced
Treatise, Vo. 4B, G. C. Ainsworth et al. (eds.), Academic Press,
New York, pp. 113-144.
Ellenbogen, B. B. et al. (1969) "Polyunsaturated fatty acids of
aquatic fungi: possible phylogenetic significance." Comp. Biochem.
Physiol. 29:805-811.
Emerson, R. (1950) "Current trends of experimental research in the
aquatic Physomycetes." Ann. Rev. Micro. 4:169-200.
Erwin, J. (1973). "Comparative biochemistry of fatty acids in
eukaryotic microorganisms." In: Lipids and Biomembranes of
Eukaryotic Microorganisms, J. Erwin (ed.), Academic Press, New
York, pp. 41-143.
Findlay, R. H. et al. (1986) "Biochemical indicators of the role of
fungi and Thraustrochytrids in mangrove detrital systems." In: The
Biology of Marine Fungi, S. T. Moss (ed.), Cambridge University
Press, London, pp. 91-103.
Fuller, M. S. et al. (1964) "Isolation and pure culture of marine
Phycomycetes." Mycologia 56:745-756.
Gellerman, J. L. & Schlenk, H. (1979) "Methyl-directed
desaturation of arachidonic to eicosapentaenoic acid int eh fungus,
Saprolengnia par asitica." Biochem. Biophys. Acta 573:23-30.
Goldstein, S. (1963) "Development and nutrition of new species of
Thraustochytrium." Am. J. Bot. 50:271-279.
Goldstein, S. et al. (1969) "Biology of a problematic marine
fungus, Dermocystidium sp. II. Nutrition and repiration." Mycologia
61:468-72.
Hori, H. et al. (1980) Nucl. Acids Res. 8:5535-5539.
Hunter, J. E. (1987) "Fish oil and other omega-3 sources." J. Am.
Oil Chem. Soc. 64:1592-1596.
Kates, M. (1986) Techniques of LIpidology: Isolation, Analysis and
Identification of Lipids, Elsevier, Amsterdam.
Kazama, F (1980) "The zoospore of Schizoshytrium aggregatum. Can J.
Bot. 58:2434-2446.
Kyle, D. J. (1987) "Microalgae as a source of EPA-containing oils."
Abstract of talk presented at World Conference for Fats & Oils,
Hamburg, West Germany. J. Am. Oil Chem. Soc. 64:1251.
Leedale, G. (1974) "How many are the kingdoms of organisms." Taxon
23:261-270.
Lepage, G. and Roy, C. (1984) "Improved recovery of fatty acid
through direct transesterification without prior extraction or
purification." J. Lipid Res. 25:1391-1396.
Margulis, L. (1970) Origin of Eukaryotic Cell, Yale University
Press, New Haven.
Margulis, L. and Sagan, D. (1985) "Order amidst animalcules: the
Proctoctista kingdom and its undulipodiated cells." BioSystems
18:141-147.
Mannella, C. A. et al. (1987) "Interrelatedness of 5S RNA sequences
investigated by correspondence analysis." J. Mol. Evol.
24:228-235.
Moss, S. (1986) "Biology and phylogeny of the Labrinthulales and
Thraustochytriales." In: The Biology of Marine Fungi, S. T. Moss
(ed.), Cambridge University Press, London, pp. 105-130.
Perkins, F. O. (1976) "Fine structure of lower marine and estuarine
fungi." In: Recent Advances in marine Mycology, E. B. Gareth Jones
(ed.), Elek Science, pp. 279-312.
Pigot, G. M. (1989), "The need to improve omega-3 content of
cultured fish," World Aquaculture 20:63-68)
Perkins, F. (1974) "Phylogenetic considerations of the problematic
thraustochytriaceous-labrinthulid-Dermocystidium complex based on
observations of fine structure." Veroff. Inst. Meeresforsch.
Bremerh. Suppl. 5:45-63.
Pohl, P. and Zurheide, F. (1979) "Fatty acids and lipids of marine
algae and the control of their biosynthesis by environmental
factors." In: Marine Algae in Pharmaceutical Science, H. Hoppe et
al. (eds.), W. de Gruyter, Berlin, pp. 473-524.
Poyton, R. (1970) "The characteristization of Hyallochlorella
marina gen. et sp. nov. a new colorless counterpart of Chlorella."
J. Gen. Microbiol. 62:171-188.
Pyther, J. H. (1983) "Cultivation of Macroscopic marine algae." In:
Solar Energy Research Institute Aquatic Species Program Review.
Proc of the March 1983 Principal Investigators Meeting.
SERI/CP-231-1946, pp. 7914 88.
Sargent, J. eg al. (1989), "The lipids," in Fish Nutrition, Second
Edition, J. Halver (ed.), Academic Press, pp. 153-218.
Schlenk, H. (1954) "Urea inclusion compounds of fatty acids." Prog.
Chem. Fats and Other Lipids 2:243:267.
Schneider, J. (1976) "Cultivation of Microorganisms. Section 3.2:
Fung." In: Marine Ecology, Vol. 3, Part 1. Cultivation, O. Kinne
(ed.), Wiley Interscience.
Sigma Chemical Co. (1988). Catalog: Biochemical and Organic
Compounds for Research. Sigma Chemical Co., St. Louis, Mo.
Simopoulos, A. P. et al. (1986) Health Effects of Polyunsaturated
Fatty Acids in Seafoods, Academic Press, New York.
Sorokin, C. (1973) "Growth measurements: dry weight packed cell
volume, and optical density." In: Handbook of Phycological Methods:
Culture Methods and Growth Measurements, J. R. Stein (ed.),
Cambridge University press, Cambridge, pp. 321-343.
Sparrow, F. K. (1960) Aquatic Phycomycetes. University of Michigan
Press, Ann Arbor, pp.. 37-38.
Wassef, M. (1977) "Fungal lipids." Adv. Lipid Res. 15:159-232.
Wette, J. D. (1980) Lipid Biochemistry of Fungi and Other
Organisms. Plenum Press, New York.
Yamada, H. et al. (1987) "Production of arachidonic acid and
eicosapentaenoic acid by microorganisms." Abstract of talk
presented at Wold Conference for Fats & Oils, Hamburg, West
Germany. J. Am Oil Chem. Soc. 64:1254.
* * * * *